This is making my head spin.....I don't think you discussed a down payment on the new coach. This is pretty simple stuff. Sell the old RV private party, unless you don't want the hassle, use the sale as the down payment. Finance for as money months as they will allow and pay as much additional money toward the pay off as you can each month.
With the above, your payments are kept low in case there is a financial emergency, yet you can pay down the principal as you can.
Lastly, shop for a loan. Good Sam is the LAST place I would look. A dealer always has several lenders available to them and they use the best lenders for those with the highest credit. Out west, Bank of America and Bank of the West are big RV lenders and offer competitive rates.