Just so you know for future shopping, there is no one thing it "takes" to put a hold on a camper. That's because each camper is sold by an individual, private seller, and everyone has their own way of doing things.
Seller A might hold a camper for you for six months on nothing but a word; Seller B might hold a camper for you with a deposit; Seller C might say they'll hold it, have someone come with cash, sell it to that person, and then say "Well, hey, first cash gets it!" And a million variations in between.
What it comes down to is that everyone is different, so there is no one method. It's best to be as clear as possible, and ask about contingencies. Usually it's just a matter of setting out how everyone expects things to go; occasionally you will deal with someone who is less than honest.
The only rule in this sort of thing, to my mind, is that there is no rule.
Lest you get the wrong idea, I've had mostly excellent experiences in buying things from private sellers over the years. A couple of bad apples but they were exceptions. BUT, almost every transaction was different, with different "rules," just depending on the seller's and my agreement and preferences.