I have never bought an RV that was less than 10 years old! My Credit Union(s) financed them all with no problem at all.
Just a few months ago, I purchased a 1999 dodge CTD truck. The Credit Union asked only one question: "How much do you want the payment to be? OK, sign here!" Done deal, go get the truck.
IMO, based purely on personal experience, a Credit Union is the only way to go to finance ANY vehicle!
I probably don't need to point out that if the RV is self-contained, and is collateral for the loan, the interest is usually tax deductible as a second or vacation home. The interest on a personal loan of any kind is usually NOT deductible!