You should be fine with Meguiar's Ultimate polish as it is not particularly abrasive unlike some others. However, may be worth considering something like Autoglym Super Resin Polish as that is very non-abrasive. You just want to be careful with caravans as the paint is fairly thin.
Of course though, remember that polishes give very little protection - they may leave a slight protective layer of waxes that is short lasting, but nowhere near as good as a hard wax. So if you are using the polish with a view to protecting the caravan, you may be best thinking again. Polishes are really for removing defects (due to their abrasive nature and filling minor scratches with the fillers they contain), prior to applying a wax.
Autoglym HD wax is very reasonably priced and easy to apply. When I do my caravan, I do a very good wash and then sometimes wipe the dirtiest areas with a clay mitt (although I tend to be lazy with this on the caravan), then do a gentle machine polish with Autoglym SRP followed by a layer or two (depending if I can be bothered to do 2 layers) of HD Wax. Sorry, that was a bit of a long post!