Google RV Financing and get rate quotes from several of the lendors specializing in RVs. Essex, Beacon Credit, Fun-loan.com are some of the big ones.
Good Sam and FMCA both have working arrangements with lendors and you get good service through them - if you are a member of eiher one, atke advantage of it.
I've used Bank of America for my last two loans and had excellent results. Both were arranged through a dealer, but they didn't get me a good rate until I brought in a better rate quote from another company. Once I had a better rate quoted, BOA & the dealer matched it.