Longer wheelbase will be a little bit more stable.
Long box (8 ft) will leave more room between the pin / FW and the corners of the cab. This will almost always allow sharp turns without hitting the cab. Sharpest turns are when backing into a space.
Regular box (6 ? ft) is shorter (DUH). With older FW with a straight front (side to side) profile, the cab would frequently hit the cab on sharp turns. Most newer FW have some type of curved or tapered lower front corners to allow sharp turns without hitting the cab.
For short box (5 ? ft), the problem is very real.
Solutions include a slider hitch, a Pull Rite style hitch that slides automatically, or go with a regular hitch and be careful. Many folks report never needing anything special when towing with a regular box.
It all depends on specifically what truck, what hitch and what camper.