Seems to me that screwing some MDF covered in parcel tape onto the "smooth" side seems like the best bet, as it gives you a good strong surface to press against, to get the bubbles out, as it can take a fair amount of pressure, especially if it's your first go. A wall-papering seam roller (1 inch wide) would be my recommendation. Definitely rough-file the edges, and pre-trim all the layers of chop-strand matt or glass cloth before you mix the epoxy. CSM works better with sharp curves, so you might want both CSM for the first layer, then woven roving for the reinforcing layers. I'd then wait 2 days (as it's cold atm), remove the MDF and fill the imperfections on the smooth side with gel coat or a coloured layer of epoxy.
Good luck
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