Gel coat is a top coat and I doubt that is what you have. I haven't done alot but the way I did it was. Put down a coat of resin and while it is still wet place the fibreglass mat into it add a little more resin and work out all the air bubbles before it drys. When it is dry cut out all the air bubbles and replace the missing cloth with the same method.
Do a top coat with the same resin that has been tinted by the same supplier. Gel coat is the shiny layer that you would see on a boat.
I would think when you find a supplier, matching colour will not be a problem. You could grind or sand away the real rough spots and replace cloth that gets removed. Run some tape along the bottom of the aluminium and run fibreglass right up to it. Cut along that line and remove the tape and then caulk between the fiberglass and aluminium. This stuff has a min temp to work with so you may have to build a tent and supply some heat.