Being from the JEEP TRAIL days of the 60s we all always like to mount the gas cans around the spare tire mounts. There was all kinds of spare tire mounts available back then.
I use my pickup truck bed today where I also carry my 2KW Honda Generator in the front tail gate area. My truck bed has the heavy duty locking folding hard panels that keep everything safe and out-of-sight in my truck bed. My generator goes where I go and is secured and out-of-sight when not in use.
I don't know how far along you are with your JAYCO X213 and I can see you are wanting to do alot of camping off the power but I would want to use the area between the X213 front diamond plate trim and the Propane tanks to mount a 48-inch truck side bed lockable storage box to house my four each GC2 6V batteries to give me 450AHs battery capacity for camping off the power grids... To me this would have the priority of where to mount the Jeri-cans... To be successful about camping off the power grid you will need to do several mods to your X213 to gain smart mode technology and using inverter etc to be able to operate all of your 120VAC and 12VDC toys you have. I work on the game plan of having my battery banks large enough to do all of these things and then re-charge my battery bank the next morning with a direct connect to my 2KW generator which is secured at the truck bed tail gate area.
You could extend out from the sides of the Battery Box and mount a Jeri can on each side I suppose.
The area on the rear bumper of the X213 below the rear bed slide is another nice looking spot for the spare tire and Jeri-cans but alot of folks are getting awa form mounting anything on the rear of the trailers because of rear end accidents. This is also where you sleep so having jeri-cans under your bed may be a concern also...
I saw you mentioned the KAYAKS. I guess you are wanting to mount them on top of your truck and maybe extend out over the cab area with the mounts... Have seen a few of those that looked great... Going this route might also be a good spot to mount some jeri-cans.
I like how the guys from Australia take on the jeri-cans with their off-road trailers. They have it all built-in real nice
sample photos from google images