Actually it's not really unwarranted. In most manuals that come with fiberglass boats it will clearly state not to use abrasive pads, chemicals, acids, cleaning products containing corrosive agents or abrasive cleaners. As you have a trailer that isn't that old comparatively the less harsh products you use on the gelcoat the better if you are wishing to get the coat to shine up on its own without taking the last resort approach of putting floor wax on it that many here have taken. Due to the age of your trailer you really should be able using products designed for use on gelcoat be able to get it nice & shinny again. Yes some of the fiberglass specific products do contain some abrasive compounds but the over the counter ones such as the cleaners & wax ones are on the light
side & result it very little gelcoat loss & the theory being you should only need to do a complete cleaning with compound agents a few times over the course of many years if you keep the fiberglass well waxed. I used a light
fiberglass compound on my trailer 5 years ago & it's only required a good waxing each year to bring the shine back. Products such as Bar Keepers friend contain other cleaning agents and on the abrasive scale are getting up there.