I don't have a 5er, but I've read a lot from the 5er forum. Seems one item to watch for with a short bed is the distance from the corner of the truck cab to the corner edge of the 5er so they do not hit. With a short bed, you may not be able to make a 90 degree.
However, there are those who successfully use a slider hitch with no problems with a short bed. So, I would think you should consider 2 options:
1: Long bed with a fixed 5er hitch
or
2: Short bed with a slider 5er hitch
Regardless of which set-up you get, you always have to watch the corner of your camper and the corner of your truck cab. With a TT, we always have to watch jack-knifing (regardless of long OR short bed), which can do a whole lot of ugly pain too.
