A friend of mine used dope on his boat. It got it to the water in a hurry, since it dries very quicky. However, it hasn't proven to be very durable.

On my own boat, I used 3 coats of satin polyurethane over the polyester fabric. So far, it's been pretty rugged, though I think one more coat would be wise. I don't see why 8-10 coats of varnish would be necessary. You're only trying to seal the fabric, not make it look like a coffee table.