Does the expense of renting an RV pay off in the buying process? The answer to that question is complex and depends largely on your personal situation and preferences. My wife and I faced the same question about 2 years ago. On two occasions, we rented (two different) 45 foot pushers for a month at a time. The experience did result in some changes when we eventually purchased our first RV. However, I question whether the expense was worth it, as I doubt that our purchase would have been a disaster if we had not rented.
What did we learn from our rental experience?
For our purposes, we do not need 45 feet (we bought a 40 DP with a floorplan we like). We much prefer flat towing (definitely worth the cost of vehicle prep). We like the dinette (rather than booth). Spacious shower and toilet area is important to us. In places we tend to travel, 3 roof a/c units are a must.
The comments regarding the RV learning curve are valid. We seem to be enjoying each trip more than the last. The curve is especially steep the first month.
We became interested in RVing for sightseeing. While renting, we unexpectedly stunbled upon the best reason for buying an RV .... the people. Almost everywhere we visit, we meet friendly people.