We used to rent an RV before we got one, and we always went with Cruise Canada/Cruise America.
They were really friendly and RVS were always in pretty good condition, but this was about ten years ago, don't know about how the company is like now. Still worth it to check out though IMO.
http://www.cruisecanada.com/rent/
Be prepared for your wallet to get a lot lighter from the gas, we used to only get around 3 kms / L.
Have fun!