Absolute first thought that popped into my head after looking at the photo:
How tall were these people?!?!?!? That shower pan is sitting on TOP of the seat! That should give somebody just about 4 feet of "headroom" to shower in. On top of that the shower pan is awfully tiny.
I wouldn't want to climb up that high for the toilet either...
OK, second thought:
How rough/hard is the bedliner stuff? Would it be acceptable if it was just painted over (and over and over)?
Heavy Duty Construction Adhesive (in the caulk-gun tubes). I used it in the Boler
to re-stick ensolite to the walls. I also used it in the PlayPac to stick carpet to the bare fiberglass walls. I've also used it in the current baby trailer to stick wood furring strips to the walls. It's great stuff. (Well, "Great Stuff " is also great stuff - but this is good too)
How about simply upholstering the ugly-ed up part? Cover it with the same material you use for the seat cushions - add some padding and a couple buttons and it looks like it's supposed to be there and not like it's only there to cover up the ugly.