this is to keep the car in the elements when not in use with and without the top/doors..Is this to keep the rain out when the top and doors are off or is this to protect the paint from the sun? If it's just for the rain when the top is off I had a nice tarp I kept in my TJ for this purpose. I only used it as a temporary thing, like when camping, so I had found some leveling blocks I was able to tie some coradage around, I'd lay those in front of the tires and drive onto them then tie the tarp to those as my main hold downs. My TJ had a brush guard I could tie the front middle of the tarp to and I tied the rear middle to the tow hitch. Not keeping animals out, but it kept the seats dry and seemed to help with the dust as well. What I liked most about it was a good tarp has a ton of uses and I often set it up to also work as a canopy I could sit under if it was raining rather than sitting in my little tent. I'm sure you could come up with something similar for the JL (and I plan to myself) if this is what you're needing.
I'm a fan of aquaquest tarps. https://aquaquestwaterproof.com/collections/waterproof-tarps