I always thought something like this was a great layout for truck bed storage boxes...

Google Image
My truck bed uses the FOLD-A-COVER brand hard folding panels which would work just fine with the above shown type boxes with the fifthe wheel hitch. the hard folding panels will stackup behind the truck rear window and not interfere with the fifth wheel hitch operation...

Google Image
Then when you have your fifth wheel setup at the camp site you can totally enclose your truck bed for more security for storage of things...
Roy Ken