I've seen , metal casters and rollers mounted, to the rear bumpers of 5th wheels and TT's. Never done it myself.
First question. How much stress are you going to be putting on the end of the frame rails? No sense doing this if your going to damage the RV.
Second. How much clearance do you have between the sides of the pick-up box and the underside of the front corners of your 5er; when you get to the place at your driveway where you need the bumper to lift? No sense damaging the truck either.
I had a sharp , de-cline , to the drive way at my last house with a 5er, and had to ramp the front wheels of the truck, to stop contact between the box corners and the underside of the 5er. After the first time.
If this is the only spot your having trouble , ramps for the 5er wheels might be a safer option.