I can add that there’s a lot of supposition in the replies. Has been my experience in several different states that it’s no problem re-titling a vehicle that has a title from an owner previous to the seller.
OP, if it’s the right camper, then get it. As long as the title is endorsed properly and is a legit title you won’t have any problems in OR or WA and any other state I’ve lived in.
Heck that’s how most old junk like vehicles and campers end up anyways. It’s not uncommon and it’s not illegal, whatever. And you certainly won’t be on the hook for any back fees for a vehicle you didn’t own when the fees were incurred.