Don't be surprised if the dealer won't let you take a "test drive" with the camper in your truck before you buy. I asked a dealer this just before I was ready to sign a deal on a used Artic Fox camper I really liked. I wanted to make certain my truck would handle the weight okay. The sales manager refused and said something along the lines of "son, your just too much trouble and not worth it..." to which I promptly got up and walked out of the office very upset. I'm nobody's son but my father's and I told him there was no way I was going to sign a purchase contract from a dealer before finding out how my truck handled the weight. In the end I found my Bigfoot camper from private party and couldn't be happier.
I think the issue was the usual liability issues (maybe it being a used camper perhaps on consignment is what stopped them) that our country's lawyers have managed to ruin our great country over but that is a screed for another day...
Needless to see, this very well could be just my experience from one dealer and there may be other dealers who will absolutely let you take a test drive. Just be aware that they might say no.