Liz, this is a really interesting subject. Late model trailers (five years or newer) are typically a steal at NADA. Real world is that they just don't depreciate. If you can find one on an RV dealer's lot and get one there for NADA, that's the way to go. You'll have instant equity.
Don't give up on just one lender. We had our first credit union tell us that they wouldn't loan on a brand new '06
Bigfoot because the dealer wanted more than the trailer "booked" at, even though it was several thousands less than "sticker" price. It's a wierd world.
Our other credit union wrote the check and asked for us to send the
title. It was literally that easy, and at an excellent interest rate.
Older trailers may be significantly more difficult to finance, and you may need to look at alternative methods for that.
Good luck!
Roger