Ron, I see two problems with your idea (1) how are you going to get the tire up and down off the roof. (2) I don't think the roof of the jeep can handle that much weight safely. They do make a mount that is part of the trailer hitch I think this would be a better solution. Check it out at (
www.rvtirecarrier.com) also you can still tow with it and a lot less height to lift the tire.
Earl