Hi all, just joined ...
I have those rear boxes on a '15 Hallmark K2 along with the the rear platform & higher mounted jacks you describe all carried by a Gen1 Tundra double-cab 6.5' bed.
I find them highly useful to carry the handy-dandy EU2000i in the right box and 5 lb. gas bottle, gas grill and grey water catch plastics/hoses in the left (so chosen to balance out weight) in the left one. When traveling in cold weather with less outdoor cooking, the left box hosts a second 20 lb. bottle so I can run heat 5-7 days in 10-20 deg. F temps. before having to top back up.
To keep the cargo from flopping around on rougher roads, I cut up some of those rubberized foot mats found at the local hardware joint to fit the bottom to cushion the cargo (with pattern side down keep stuff out of any water that oozes in). The boxes are not water-tight but will drain what little water gets in with any nose-up attitude of the vehicle. The generator and other items in the boxes get packing stuffed around them (cut up pieces of camping foam sleeping pad) to keep everything firm and prevent jostling. Loose stuff will beat up the boxes and everything else inside.
I'm have 200W of solar up top and only need to use the generator for AC/microwave in warm months, but during the days of long shadows, grey skies and running all systems I'll need to pull out the trusty Honda and bump the batteries by running on eco-throttle for 20-30 min. each day. Sure is nice to have at the ready to pull out, fire up, juice the batteries, shut off, let cool and slide back in to keep 'er all operational. Having backup gas to prevent furnus interruptus when chilly is priceless in and of itself!
Being all the way at the back, I'd limit the loading to no more than 50 lbs or thereabouts though...
