All of the suggestions immediately above are excellent!
It's almost impossible to get a good deal on a used motorhome (or a new one) from a dealer if you close the deal in one or even two visits. The dealer is NOT going to let an interested buyer go just because the buyer doesn't like the asking price. Negotiating price is what dealers do.
It's a game of wits and most successful dealers are not only very good at it - they also enjoy it. The better you are at convincing them you are interested in a "fair" (to you) deal that you can afford, but may walk away for good if you don't get one, the better deal you will get. It's also a good idea to get your financing in line, at the best interest rate, before you close the deal. Then let them know you'll be happy to finance with their lender if they meet or beat the loan terms you've found.