I read in a book or magazine article (sorry, don't remember which one) that the fill coats do very little in the way of strength - they are primarily to fill the weave of the cloth to give a smooth finish. Without fill coats, you will not be able to sand the epoxy without cutting into the glass. And that will seriously weaken the boat. The book recommended not doing fill coats on the inside of the hull and deck to save weight, material, and time. On the inside, a real smooth surface isn't required, and you won't be sanding there.

I also used 3.2 oz satin weave cloth on my kayaks. I found 2 or 3 fill coats filled the weave, and allowed me to sand without cutting into the glass. The key is, of course, to avoid those sags and runs that require excessive sanding. Many sources recommend foam rollers, and tipping out with a brush. I found that foam rollers applied too much epoxy, and I ended up with runs. I got some rollers called "The Applicator" from Jamestown Distributors. "The Applicator" is a short bristle roller designed (according to Jamestown's catalog) for use with epoxy. Using this roller and tipping out with a brush, I was able to eliminate most runs. And if you do get some runs and sags, use a scraper to remove them before the epoxy fully cures - much quicker and easier than sanding.

Ken