I don't know if it's too late on this thread, but if you check out some of the newer trucks from Ram and Ford, they both have a 5th Wheel Prep package available. It means that you can get a 5th Wheel hitch that will drop right into the truck - bedliner or no. Since it's a factory system rigged to the frame, it's about as good as it gets.

I just saw that your signature has an added 2014 Ram Laramie Mega Cab 3500 DRW. If you did get the 5th Wheel prep kit, you can look at a list of the available options I'm keeping updated at http://www.ramgunner.com/ram5thwheel.htm