You're wise to be careful.
Just curious since the ones you mentioned were private parties. I would not discount the option of buying from a dealer if they have what you want.
You're less likely to see an ad that says "mint" and have it turn out as a a total wreck with a dealership. And at least if something is wrong with a camper at a dealership, you might be able to work the cost of fixing it into price you want to pay.
I've not heard any horror stories about dealers selling campers with dodgy titles (not that it couldn't happen.)
Private parties, Craigslist, RVTrader and dealerships - all have their pros and cons.