IMO, every deal is different. Monthly payments are just one aspect of owning/buying an RV if you plan to finance it.
For example, some loans use a trade in instead of a down payment (or both) as part of the purchase price. Some loans have variable interest rates and a balloon payment at the end. Some are "interest only" or even negatively amortizing. Some loans include insurance or extended warranties in the purchase price, others do not.
Everything varies based on the dealers need to sell something, TODAY, what is on, or, on the way to the dealers lot, interest rates, your credit rating, your income, your trade in, time of year, the economy, etc., etc., etc.
Based on your particular circumstances, YOU have to negotiate the best deal (for you) that you can. There are no "standard deals."
Chum lee