Polyester resins are not designed to cure in the presence of air, which considering that you'll have exposed resin on one side and breathable fabric on the other, means that it probably won't cure at all. They're also pretty nasty to work with due to the strong fumes.

One-part polyurethanes are less durable than two part, but they're much less expensive and very easy to work with. Zar exterior oil-based poly' is among the best of the one-part products. It's slow drying, so the rule is one coat per day for however many coats you want to apply. I find that three coats seals the skin well and 4 produces a pretty smooth finish, with some weave texture still present. Zar is also easy to tint using artist's oil colors. Overall, it's a very easy product to work with.