Personally, I think long-term RV financing has been a genius move by the RV sellers.
Without it, given the massive depreciation of RVs when you drive them off the lot, used RVs would always be preferable to new. You could buy a 5-year-old model for substantially cheaper than new, and there would likely be a huge supply of them given the people who get in to RVs and then discover they can't afford it or they don't use it as much as they thought they would.
But with long-term financing, people are upside down on their loan long enough that by the time they aren't the RV is no longer that attractive as a used buy. So they can't afford to sell it, and no one wants to buy it at payoff value since it's so close to the price of a new one.
So by allowing long-term financing dealers have shut down the used market for models new enough to compete with new.