Skirt construction attempt, Take 2:
Got a decent (smooth, non creased) cardboard mockup taped into place on the frame & wheel arch, then stuck the first layer of glass mat to it with polyester resin. Should be able to get another layer on this evening. Slow cure time with the cool temps these days (about 9 C).
Orange: I agree epoxy resin is best, for several reasons - I've used it on boats before. But the "experimental" nature of my car fabrication mods makes me want to keep the costs down. I'm never sure if they're going to turn out or not.