We're renting from Greenberg RV this August. It is our first time, so I can't vouch for the quality, but prior posts have indicated people seem to like them.
There are several companies that rent RVs and offer delivery and setup at the fort. Google Fort Wilderness RV Rental and you will find all of them. We have rented twice from www.greenbergrvflorida.com and had a great time both trips. We picked Greenburg because they had so many different models to pick from, most are new or not over a year old. Other companies either didn't list the model year or they were 2005-06 models which is something I didn't want. Greenberg has a great web site that will answer all your questions.