Do you have something mounted under your passenger seat?
Not mounted, but it is stuffed too. I've had 13 years with this truck to work out how & where to pack things. Refine and condense, refine and condense, etc. The race/chase tool bag goes with me on any trip, so I do have the small jumpers along, but in an '84 Toyota there just isn't the room the full sizes have.
Ramblin',
Winching is a lot more like starting so any battery intended to see winch loads should probably be a starting type battery rather than a deep cycle type battery. Not that a deep cycle won't run a winch (been done a lot), but that relatively short bursts of high current is what a winch wants and what a starting battery can best supply. If you foresee that you'll be winching with any regularity I think the starting battery is the better choice to connect it to.
I also think that the battery in the camper should remain the primary camper battery. That allows the aux battery under the hood to be the back-up for both starting and for the camper without having to run large, starting current capacity battery cables to the camper.
The thing about marine switches is that they don't switch themselves. If you are absolutely anal about checking and setting such things then you could build the system using only manual switches. If you are like me and not consistently anal enough about such things then I would suggest looking into the Automatic Charge Relays / Voltage Sensing Relays as these do the switching for you based on if the alternator is putting out voltage or not. Can easily wire these in parallel with a marine manual switch so that you have redundancy and self jump-start capability. I know that
BEP Marine offers just such a combo package and I think that Blue Seas does as well.
The issue becomes separating all three batteries. Two is easy, 3 can be a little more involved to a lot more involved depending on where you want to control this from and how.
One method would be to use the VSR/switch linked above to charge the under-hood aux battery and the camper battery. Then in the wire between the under-hood aux. and the camper batteries have a Cole-Hersee constant duty solenoid activated by the ign switch in run mode. In parallel with the solenoid have an manual switch. This way the two aux batteries are combined with the ign on and the VSR takes over making sure that they're charged.
Turning off the ign disconnects both the VSR and the solenoid, so now each battery is isolated from the others. Turning on either manual switch will connect the two batteries immediately on either side of it together. You would need to either run very large cable to the camper battery or be Extremely careful to never try to start the engine with both manual switches turned on. A safety that could be installed would be to put a large amp Maxi fuse (or similar) somewhere between the under-hood battery and the camper battery. Size it and the wire or cable to be safe with maximum alternator output, plus a little extra for a margin. With the fuse in the system should you try to start with all of the manual switches turned on the fuse will blow if more current than the wire or cable can handle is demanded from the camper battery.
The more that I think on it, this is how I would set it up if I did not simply make both batteries under the hood into a single battery bank.