I have used the hard folding panels with the 5th wheel and it worked great. Everything folded up just behind the truck rear window and snapped in place. I also have a tool box in this area as well...
This is called the FOLD-A-COVER G4 ELITE
I too like to cover my entire truck bed when unhooked from the trailer...
All locks down for me with my setup... Pretty good weather seal wise as well...

You can get pretty fancy with a fifth wheel setup with additional tool boxes etc as long as they all do not extend up above the bed rails like this google image shows...

Roy Ken