Make sure the seller shows you ALL the systems before you leave with your new camper. Go to the manufacturer's website or YouTube and familiarize yourself with the camper before you go and pick it up. Make a list of things to pay special attention to (holding tanks, water fill, dumping, for instance).
Reason I'm saying this: it's what I wish I had done better at when I bought mine!
Truck campers are great. You can overnight in truck stop restaurant parking lots, or the Crackerbarrel. Nobody will come knocking on your door, as long as you ask permission from the manager. It also helps to leave a receipt from the restaurant on your dashboard so the security peeps know you're a legit customer.
The Dire Wolfess