Ok, I have never done this, but it sounds intriguing. A Czech buddy of mine who built kayaks back when they were (and racing kayaks still are) fiberglass was in TAP Plastics the other day, and was told that you can hand lay up and then put mylar over the wet lay up then squeegee the mylar and you will (or can if done properly)get a shiny "inside-the-mold-like" shiny finish when you peel the mylar off.
But epoxy sticks to everything! So, I think I would call TAP about this before doing it to make sure that you can actually peel off the mylar!!!
Epoxy does not stick to everything. It doesn't stick to anything with a wax surface. It doesn't stick to visqueen and other such plastics. Vacuum bagging works because of this. Vacuum bagging uses peel ply which allows the resin to pass through to the absorbent fabric on the other side, then a plastic sheet like visqueen seals the air. Not only can you peel off the visqueen easily, without wax, but you can also peel off the peel ply and it has resin inside of it. You can also remove the epoxy part from the waxed mold.
You can get a glossy finish by covering it in plastic. I did this with my rear sponsons. I put down plastic, then glass, then plastic, then piled cinder blocks on top. I got a smooth 2-sided finish from a simple compression mold.
However the finish will only be as good as the layup. Any wrinkles in the plastic will cause blemishes in the finish. It also will not correct any blemishes causes by uneven plug or uneven fabric thickness in the layup. Remember the OP is trying to fix divits and dimples in the base fabric. Plastic will not fix those. Resin is not UV resistant so you should be prepping it for paint/primer anyway.
I have brushed on epoxy and allowed it to cure for a smooth finish. I usually use this to seal my plugs since I like to use drywall mud to build them. A few important notes.
Cheap chip brushes loose their bristles. They are an absolute MOFO to sand out. Don't use habor freight chip brushes to brush on plain epoxy (although they are great for laying up fabric). Use better quality $2-3 chip brushes so they don't loose their bristles.
I actually prefer the foam style brushes. I'm not sure if the foam brushes will hold up to poly or vinyl resins so you need to test that. I have only used it with epoxy to seal my plugs (poly and vinyl melt exposed foam).
Use a heat gun. Resin gets more viscouis when heating. This helps it lay smoother and takes out the bubbles. Just remember you will get sags on vertical surfaces. Also realize it cures exponentially faster after 70 degrees, so don't heat the pot or you wont have time to get it down.
