To remove paint and then have the trailer gel coat redone would probably be too costly.  Your best option is to repaint with a quality marine paint.  It can be done yourself with rollers and there are numerous write-ups about how to do it. I've seen some excellent results of trailers that were rollered with the marine paint but the paint is very expensive although this is probably the cheapest route. A good fiberglass/auto shop for a painting estimate would probably be better.  You need a shop that specializes in fiberglass for estimates.  That probably will be fairly pricey, but pros would be doing it. I'd need to see pics of the trailer to be able to tell more.

The zip lock trim is available from Scamp Parts and probably best place to get it.  Not too expensive.  

You need a zip lock trim tool and those can be a bit difficult to find, I did find the exact one I used at Amazon:

Lisle 47000 Windshield Locking Strip Tool

I did both my front and rear plexi windows on my Scamp 13 redo and it is not a job for the faint of heart.  I will try and locate my write up from that repair, but it took about 2+ hours of hard labor per window with lots of opportunites to really screw it up.  Once you learn the technique on the first window the second one goes a bit easier.  It is the one job that most Scamp people say after they do it, they would never do it again.