It's not a waste of money compared with the cost of buying one and then deciding it's not quite right. We bought a used Chausson only to discover later that it didn't suit us. A month later the dealer we bought it from had an almost identical camper - same make, same year, same mileage, same length, in fact the only difference was the L at the end of the model whereas ours had an S at the end of the model, as well as the inside layout we wanted. It was priced exactly the same as we had paid for ours.
So I returned to the dealer and said we would prefer that one. How much do you want to change? I was hoping it would only be £5k which we would have paid.
"£15,000 plus yours."
That's a LOT LOT more than it would have cost us to rent it for a month. And it also tells you what sort of profit they are making. We won't be going near that dealer again.