I'd hazard that financing of not, buying an RV is a losing proposition, financially, for nearly everyone. (I'm sure someone will find an exception, but that would be rare.) For most people, refusing to buy until they could afford to pay cash would result in a large opportunity cost - they might not be able to do it until the kids are teenagers, or gone, or might never be able to get one at all.
Recommending such a thing as The Way to do it is, IMO, a form of elitism - wanting to restrict the owning of an RV only to those with a high enough income or other available resources to be able to pay cash.
Disclaimer: I financed both of my trailers for 10 years. In both cases, I paid them off early - 2 and 3 years respectively. I financed them the way I did because I wanted more control over my cash flow (which varies seasonally, and somewhat unpredictably).
