I can guarantee you that you will need more than 50' of turn radius at some point. I own a fifth and would never go into a campground with only that little turning radius. As for your pin box hitting your bed rail it shouldn't but depending on the type of pin box, this might be an issue, pictures would really help. What I would do is get the wife or someone your trust to watch your pin box and bed rail clearance while you back up and turn to see if there is a clearance issue, if not, you're laughing, if there is you really only have two options, raise you hitch a setting or two, yes this will throw out your level, not the choice I would go with. I would look for a new pin box to fit your application change your pin box to a type with a greater drop at the king pin. these boxes cost $1100 and up not really cheap but when compared to the cost of your rig it a small amount to pay in the grand scheme of things. Hope this helps let us know what you do and again pics would help.
"Never forget the trip is as important as the destination"
2014 Ram 3500 Laramie 4X4 CTD
2011 Dutchmen Denali 262 RLX