I have a motorhome and this question comes up periodically on
www.rv.net. I doubt you will find an individual to rent you their rv. It just wouldn't be worth their time to rent for the peak season. Also rv's need hookups. You would need at least a 30 amp hookup, which if ask an electrician to install one he will probably put in a dryer or welder service, which will smoke the rv. They need water and a sewer connection so you can dump the tanks.
Renting from Camping world in Chichester maybe a possibility. They may give you a good long term deal. If not if you buy right, you may be able to sell after a couple of months and have it cost less then renting.