Recommended storage in bed with 5th wheel

I would leave well enough alone!

An auxiliary fuel tank, and a case of drinking water.

Personally I like my bed height 30” front to back Highway Products tool box. I keep a 5 full of diesel when towing. May go to a TITAN 55 gallon replacement tank.

I use 2X12s built like a ladder with three steps laid down on it's side.
I only use it on trips longer than several weeks in tandem with a tool box against the front of the bed that leaves a gap on each side of it.
The gap on one side is the Champion 2000 watt genset, the other side is a 5 gallon gas can to feed it if necessary.
Behind that is the 2X12 thing. 5 gallon diesel cans sit on each end where I can reach them, with a 20lb propane tank and a 6 gallon water tote in the other 2 holes. All of that is in front of the hitch.
A tonneau covers all of it when parked or checking out the surroundings after we get set up. It's light enough to easily remove in-between trips if I need the full bed. The truck is rarely used other than as a mule. The hitch usually hangs on the 5er when at home.

We only have a tool box in our TV bed, that leaves room for extra cases of bottled water and firewood, stuff that clears the FW hitch and overhang. We also have storage pockets that keep things from sliding around, on both sides.

Back when I had a 5th wheel, I put an American Tank (in Frisco, TX ???) 60 gallon tank / toolbox combo in the back of the F350 w / 8' bed. Served all of my needs and, combined with the truck tank, gave me circa 1100 miles towing....which meant I could always fill up after dropping the 5ver for the night rather than ever having to fill up on the road.

Guess I'm odd man out. Depending on where we go, firewood up front, tire step thingy just behind it leaning up against side of box so I can reach it, then wood blocks behind hitch for legs. If no firewood, then front is wide open. Covered w/ Access tonneau cover otherwise.

We used to carry a couple 5 gallon fuel jugs and a pair of Honda Generators in the truck bed with our fifth wheel.