I do not have a fiberglass trailer, I have a metal sided TT. I used Ibiz IBIZ World Class Wax
the day we brought the new trailer home. They have a special wash mixture to use and then you apply the wax. It goes on easy and you wipe it off while still wet. I was able to do a 26ft TT in about 3 hours, done. For spot cleaning inbetween washes they have a waterless wash/wax the buffs the unit back to clean. This product is endorsed by the Covette Club of America and the Antique Auto Club. I would not use anything else now.