There are lots of sealants out there. Tried a few but for the past 10-15 years on boats & RV the main products to use have been 3M cleaner wax (takes care of smudges & minor chalking), followed by Meguires Flagship wax (for a high gloss durable shine).
Front cap gets the treatment twice a year. The rest of the trailer gets waxed once a year. Trailer is now 13 years old & looking great. Seven month a year indoor storage helps too.
Having a good gelcoat base to work with helps too. For example I am currently doing some restoration on a 32' Albin boat that has been sitting untouched since 2007. It was looking very sad. So far just the 3M cleaner wax with amazing results on the hull.
Boat: 32' 1996 Albin 32+2, single Cummins 315hp
40+ night per year overnighter
2007 Alpenlite 34RLR
2006 Chevy 3500 LT, CC,LB 6.6L Diesel
Ham Radio: VP9KL, IRLP node 7995
