13 replies to this topic

[Nailhead]

A buddy and are going to put my camper on a '72 IH dually, and I'm trying to figure out how much support the floor will need.  The truck doesn't have a bed (it was a fire truck previously), so we're going to mount the camper on an 8'x4' welded steel subframe that will bolt to the truck frame.  Do I need to weld in multiple crossmembers (joists, if you will), or can I get away with one in the middle running fore-&-aft?

 

Thanks for any help.

[PackRat]

The wooden floor is a place where soft wood/rot can occur anywhere in the floor and more worrisome, where the floor is joined to the sidewalls. Horror stories about guys leaving the Alaskan on the jacks with the floor unsupported ended with the floor falling out of the lower section have been posted.

 

I would suggest that if you have a bare frame as you suggest, that water will make its way to the floor and floor/sidewall joints and that would be a very bad thing to do. Why not put crossmembers every two feet and then fabricate a very THICK plywood "floor" to the frame to support the Alaskan as much as possible and add "ribs" running fore and aft to keep airflow and alleviate moisture? You can read here how guys have either waterproofed the bottom of the Alaskan or used a cushion of some kind to shed water.

 

You may also want to actually weld in supports running fore and aft that the lower section can put some of the weight on if padded to prevent damage and then secure the lower section to your vehicle frame addition. All this may sound like overkill, but its easier to build preventative fixes to the vehicle than to find the unsupported floor is failing!

 

Remember....it is WATER that is the biggest enemy to the Alaskan and that includes not only the roof, windows, doors and seams, but the floor.

[Nailhead]

The wooden floor is a place where soft wood/rot can occur anywhere in the floor and more worrisome, where the floor is joined to the sidewalls. Horror stories about guys leaving the Alaskan on the jacks with the floor unsupported ended with the floor falling out of the lower section have been posted.

I would suggest that if you have a bare frame as you suggest, that water will make its way to the floor and floor/sidewall joints and that would be a very bad thing to do. Why not put crossmembers every two feet and then fabricate a very THICK plywood "floor" to the frame to support the Alaskan as much as possible and add "ribs" running fore and aft to keep airflow and alleviate moisture? You can read here how guys have either waterproofed the bottom of the Alaskan or used a cushion of some kind to shed water.

You may also want to actually weld in supports running fore and aft that the lower section can put some of the weight on if padded to prevent damage and then secure the lower section to your vehicle frame addition. All this may sound like overkill, but its easier to build preventative fixes to the vehicle than to find the unsupported floor is failing!

Remember....it is WATER that is the biggest enemy to the Alaskan and that includes not only the roof, windows, doors and seams, but the floor.

Thank you for the reply, PR.

I’m thinking I painted an unclear picture of the plan I have in mind: the floor of that camper will in no way be unsupported. I’m only trying to establish whether three joists on 24’s across, or one longitudinally would be the most effective. At this point I’m leaning toward 3 (or more— I have a bunch of 1x3 heavy wall tubing to work with) across. As understand it, the floor is 3/4 plywood, so 24” joist centers should work just fine. Most residential floors I’ve seen or built are on 24’s.

I’m a co-owner of a rain gutter company, so I’ve seen the effects of trapped water on fascia & soffit many times. We’ve made a lot of money correcting the effects of it, and that’s why I’m going to stay away from doubling up the plywood on the underside of the camper. I gave the idea some thought months back but dismissed it because it sounds like a 4x8-foot water trap to me. I will, however, go with your waterproofing idea & coat the lower section of the camper with some sort of coating. Any recommendations?

As I understand it, you’re suggesting additional support where the truck bed rails would normally be? That area will be occupied by tool boxes, and besides, as I understood it, an Alaskan camper is supposed to be supported solely by the floor, isn’t it?

As far as mounting this assembly to the truck frame, my inclination is rubber mounting it with 1/2” bolts. We haven’t really got the details ironed out yet, but once the subframe is built, we can mock it up easily enough.

Thank you for the suggestions— you pretty much convinced me joists running side-to-side are the way to go.

[Optimistic Paranoid]

As far as waterproofing the underside goes, people use various products, and seem happy with them.  I'm going to suggest that you take a look at something called BILGE PAINT, which is sold by marine paint suppliers for use on the inside bottom of boats.  It's not only waterproof, it's also highly resistant to fluids like gasoline, diesel fuel, anti-freeze, etc.

[klahanie]

 you pretty much convinced me joists running side-to-side are the way to go.

 

This. Shorter the span, the less possible defection. I've seen 16" floor spacing so would prob use at least 6 total. But your frame will be subject to a lot more movement than a house floor so there could be much more to the design, IDK.

[ArtTrek]

As far as waterproofing the underside goes, people use various products, and seem happy with them.  I'm going to suggest that you take a look at something called BILGE PAINT, which is sold by marine paint suppliers for use on the inside bottom of boats.  It's not only waterproof, it's also highly resistant to fluids like gasoline, diesel fuel, anti-freeze, etc.

Would you advise that in buying a new Alaskan, I should waterproof as well?

[Nailhead]

As far as waterproofing the underside goes, people use various products, and seem happy with them. I'm going to suggest that you take a look at something called BILGE PAINT, which is sold by marine paint suppliers for use on the inside bottom of boats. It's not only waterproof, it's also highly resistant to fluids like gasoline, diesel fuel, anti-freeze, etc.

I just gave several products a look and that idea looks promising. Add it to the task list, I guess.

Thanks!

[Nailhead]

This. Shorter the span, the less possible defection. I've seen 16" floor spacing so would prob use at least 6 total. But your frame will be subject to a lot more movement than a house floor so there could be much more to the design, IDK.

I’m trying to confine most movement to the mounting points and their rubber elements. If you think about it, that’s how pickup beds are mounted— I’m just building one without the sheet metal sides & bottom, and a lot more supporting structure.

[PackRat]

The most strain will of course be where the tiedowns are no matter how you choose to engineer them. Using a fixed bolted system to attach the bottom of the Alaskan to the frame without any rubber bushings seems to me to be the best plan. Any movement will begin the process of hogging out the holes in the floor and those four or six bolts will be where water will also want to attack the wooden floor.

 

In any event, spreading the load is advisable. For those who use a Happijac system and secure the lower section to the truck bed/frame using an eyebolt through the plywood suggest a steel baffle mounted inside the camper and secured to the plywood with an eyebolt through that and also possibly adding another baffle on the outside to sandwich the plywood. Movement in the truck bed back and forth will otherwise wallow out the hole and if it is installed and waterproofed it will last a lot longer. I suggest you see how far forward you can set the camper without scratching the cab or the front aluminum riding on the rail of the truck bed. Then add a 2x6 on edge and see if that gives you some stand-off to spread the load. Then it is time to center the camper and begin to secure it.

 

Remember to never leave the camper mounted with the truck on a downhill slope as rainwater will collect in the truck bed and water will begin its destruction of the wood! If you can park it under shelter when not in use or tarp it and the truck to keep water away from the camper completely, that's a good plan. Or...dismount it when not in use.

 

Think of your Alaskan as a wooden boat and then the apprehension about water intrusion and soft wood make sense.

[Nailhead]

The most strain will of course be where the tiedowns are no matter how you choose to engineer them. Using a fixed bolted system to attach the bottom of the Alaskan to the frame without any rubber bushings seems to me to be the best plan. Any movement will begin the process of hogging out the holes in the floor and those four or six bolts will be where water will also want to attack the wooden floor.

In any event, spreading the load is advisable. For those who use a Happijac system and secure the lower section to the truck bed/frame using an eyebolt through the plywood suggest a steel baffle mounted inside the camper and secured to the plywood with an eyebolt through that and also possibly adding another baffle on the outside to sandwich the plywood. Movement in the truck bed back and forth will otherwise wallow out the hole and if it is installed and waterproofed it will last a lot longer. I suggest you see how far forward you can set the camper without scratching the cab or the front aluminum riding on the rail of the truck bed. Then add a 2x6 on edge and see if that gives you some stand-off to spread the load. Then it is time to center the camper and begin to secure it.

Remember to never leave the camper mounted with the truck on a downhill slope as rainwater will collect in the truck bed and water will begin its destruction of the wood! If you can park it under shelter when not in use or tarp it and the truck to keep water away from the camper completely, that's a good plan. Or...dismount it when not in use.

Think of your Alaskan as a wooden boat and then the apprehension about water intrusion and soft wood make sense.

We’ll bolt the camper to the subframe at the corners (at minimum) after rubber mounting the subframe to the truck frame. I’ve got lots of metal & lots of wire to add mounting tabs, brackets, flanges, etc. where needed, so that camper will be mounted securely.

There won’t be a “bed” in the pickup sense, so none of the associated water traps. I do plan to coat the bottom of the camper with the above-suggested bilge paint, though.

Just gotta get the camper, and get this process rolling.