I really don't "get" short bed trucks. I was at the orange big box store last weekend watching some moron load about 20 sheets of plywood into a truck with a bed so short the COG of the pile of wood was only about 2" onto the tailgate. His front end was about 6" up in the air and the read springs completely collapsed and he was still loading. I''d be willing to bet that that pile of wood likely as not ended up spread across the highway. I can only imagine that most folks who buy short beds never actually carry anything back there. I have enough trouble with stuff that's too big with an 8' bed, I can't imagine going shorter.
Anyway, more on point, a long bed dually will give you lots of stability and few worries about weight limits no matter what camper you choose. If you're planning on a gigantic camper you need to pay careful attention. My truck has to serve many purposes, so unlike many here I would say it can also be right to pick the right truck and then pick a camper that will fit on it.
+1 on used, it can save you enough to pay for a very nice used camper!