Even my cheap azzed Palomino is 3/4" plywood on the bottom. sheathed in embossed aluminum sheeting with roll formed steel flanged 'U''s running lengthwise and cross ways in the front and back. screwed to the bottom every 3" with flat head wood screws dipped in sealant.
The only thing that contacts the bed of my truck is the 'U' channels. The bottom is spaced off the truck bed by 1/2" I really like the 'U' channel arrangement. Keeps the bottom off the truck bed so no damage is incurred from our wonderful rough roads and the channels add a lot of stiffness to the camper itself. Hard to beat steel for strength where it counts.
Only downside I can see is the steel is slippery but that has never been an issue yet. In fact, I removed and modified the back cross channel to carry my Stow and Go step mount.