Financing an RV is fine, if you can afford it. AND if you shopped around enough to know you are going to keep it until it is worth more than you owe on it or it is paid off.
I've seen people finance RV's and the next year decide they want something else. So they trade in and they are "upside down" on the equity. They owe more than the unit is worth. So they roll over the balance onto the next RV loan. A year or two later they do it again.
Seems the same people that do this with RV's also do it with cars.