One of the challenges you will face when replacing the bottom sheeting of choice is putting it on and making it watertight.
From the factory, the frame goes on as the final step prior to the flooring, walls, partitions etc. The floor is upside down when they run wiring, plumbing, insulation etc, and then the bottom membrane.
Then the complete frame is lowered on and fastened to the floor.
Then it gets flipped over onto the wheels for flooring and the rest of it.
This assembly process is general, and varies a bit depending on the manufacturer. I worked at a trailer factory in the early 70s and that's how it was done. The ones I worked on utilized lag bolts to fasten the frame. Most RVs I have repaired use carriage bolts through the floor to the frame outriggers.
So to attempt to replace the sheet metal, coroplast or other membrane, you are faced with cutting it around everything, making it near impossible to seal at the frame and anything hanging down.
It can be done, I have done it but it requires a lot of planning and work to disconnect the frame and jack the trailer up for access.
My 81 Citation had a galvanized steel underbelly.
