Always had my vans under cover my update (Jayco Sterling pop top ) is too high to fit in the carport. I will need to buy a cover but til then will need some polish protection.Any ideas. Have been advised marine polish is good because it contains no harsh chemicals that attack fiberglass and cause yellowing.

Correct, though it's the carnauba wax that does the yellowing. The 3M range is good quality and priced OK... though you can buy cheaper if required. Fibreglass is quite forgiving, but remember that whatever you "cut", you have to "polish". You might find that the 3M Restorer / Polish is enough on its own.

Any good quality marine fibreglass polish will protect your caravans outer surface. Take your pick. Avoid polishes with a cutting agent if your caravan doesn't need a cut & polish. We have a fibreglass caravan & boat that we've had for 15 years (the boat 15, caravan 5 years from new).