Doreen, before you undertake this realize that it will be a great deal of work and you will only get out of it what you put into it. Preparation is 99% of a successful paint job!
It isn't only the damage you can see that needs to be addressed but also the subsurface damage you can't see and this will only be obvious once you begin sanding. You may or may not be surprised!
Wash your unit well with an automotive soap and water, Scrub where necessary to remove grease and other road debris, you don't want to grind this stuff into the surface when you sand.
You don't need a stripper. You don't need bleach, mold can't digest fiberglass but it can digest dirt and debris on a fiberglass surface so wash it well.
Sand the entire unit. Unless you have structural damage, sanding should (sufficiently) eliminate surface cracking. Any cracks in the fiberglass will need to be cleaned out and fixed. Sanding removes loose surface materials to provide the surface coating (paint etc.) a secure surface to stick too. Sanding the shine from a smooth surface also promotes adhesion.
The courser the grit of the sandpaper the faster it will sand the surface however course sandpaper leaves many fine scratches which must be sanded out or filled later in the process.
Use a glazing putty to fill the imperfections after sanding. Allow to dry and sand level with the surrounding surface.
coat of primer will show any imperfections missed/needing additional putty. A heavier coat of high solids primer will help to eliminate these imperfections.
I prefer spray application but a roller can also be used. During application, try to avoid dry edges as they can show up after the paint has dried. Start at one edge/side and work toward the opposite one. You can (and should) apply additional coats of paint, as per manufacturer's specifications. Fine sanding between coats make the surface smoother and thus shine better. Fine sanding (waterpaper) after the final coat can produce a surface comparable to spraying.
When I do this I remove the windows
. This not only yields a better finished product but also allows me the opportunity to reseal the windows
, a little preventative maintenance so to speak but this is additional work and may not be something you want to undertake in addition to a paint job.