I'll jump into the breach! For cleaning, I recommend Davis Fiberglass Stain Remover. This is a blue gel, which is sworn to by most of its users. It contains a mild oxalic acid. To apply, first cover your trailer with plastic, or you'll damage the galvanized finish. Leave the plastic in place until the boat has dried following final rinse, or water will drip from the boat, pool on the trailer, and damage the galvanized finish anyway. This is a relatively mild cleaner _ I can apply it without gloves, but different people have different tolerance to acids. Suggest you wear old clothes, rubber gloves, and eye protection.
Apply with a sponge, or VERY smooth scrubbing pad which will not damage the gel coat. Unless you're absolutely certain about the pad, use the sponge. For difficult spots, use a toothbrush. Wipe on firmly. I suggest you start with the roof, work down, and do the boat in two halves, divided by the rubrail. Wash the boat with soap, rinse down, and while the boat is still wet, apply the FSR. Let the FSR dry, then rinse with water from a hose. After the rinse, a clear gel (not blue) will remain, which you just wipe off with a sponge, and then do a final, very through rinse.
Davis FSR comes in a 16 fl.oz. container, and you'll need about 20 - 25 fl. oz. to do the whole boat. So, buy two containers. You can get any number of stronger products (i.e., more acids at higher concentrations), but my experience with Davis FSR has been excellent. West Marine carries Davis, and another product under the WM brand. I suppose the WM product is basically equivalent to that of Davis, but haven't tried it, so can't make a recommendation.
As for polish, I've used Aerospace 303 for about three years, and been satisfied. You spray it on, and wipe with a cloth to smooth out. Very easy to apply, but it does require more frequent applications than some wax products. Available at WM.
Based on recommendations of others, I've now switched to Starbrite Premium Marine Polish with Teflon. It's supposed to last longer than 303, but my experience in that regard is based solely on recommendations of others. We'll have to see. Contrary to instructions, you can apply the product to the entire boat at once, although you might want to start with a small test area before reaching your own conclusion in that regard. At any rate, apply, let dry, then buff lightly with a smooth towel. It does not require machine buffing, at least when applied to gel coat which has not oxidized. Leaves a very nice finish, but doesn't make fine scratches in the colored gel coat disappear quiet as well as does 303. Like the other products, available at WM. One caveat on Premium Marine Polish: don't even think about using it on your car. The teflon leaves a haze which requires you to go back and do the whole car in about 1 sq. ft. sections. This stuff seems to be formulated more for fiberglass/gel coat, than for paint. Doesn't seem to damage paint, but it's a real pain to apply properly. I'll never try that one again.
Note: If you have gelcoat oxidization, you'll want to use something with an abrasive formulated to remove the oxidization. I don't have personal experience with those items, so will leave comment to others.
Good luck!
