I agree, I dont glass a whole plane for strength. I do it for a good paint surface. My proceedure does one coat for reson using the TP method to remove excess. Then I use hardware store light weight spackling mixed to a milky runny consistancy and rub it in with my fingers. After dry, I sand it all off down to the weave without going into the weave. Look for any spots I might have missed and do it again. Once all filled, I primer, sand, then base color. Silk will work just as good if weight is a big issue. You might even could skip the spackling and go straight to primer. This gives a pretty light weight finish if you can keep from getting too heavy handed with the spray gun.
Edwin