How do I clean and preserve the fiberglass top on my trailer?  It is "grungy" with dark gray gunk mold-like stuff.  I found a product that cleans it beautifully "Superclean by Castrol" but it also stripped the paint from the pretty teal stripe.  Luckily I had only done a small section.  Would a powerwasher work or would that damage the fiberglass?  And should I coat it with anything when it's clean?  So far I've just washed it with carwash soap. 

I used to have a trailer with a fiberglass roof.  Loved it because it didn't get hot in the Texas summers.  I didn't have a place to store it covered and it used to get some black marks on it.  Once a year I cleaned it with "black streak" remover from walmart.  Then I waxed it with automobile wax.  Seemed to do the trick for me and I only had to do it once a year.