An alternative to the spackle is to spray automotive filler primer. This will fill in the weave and any small imperfections. Wet sand the primer off until you see mostly wood, making sure that you do not sand through the glass cloth and that the surface is even and smooth. This adds a negligable amount of wieght because you sand 98% of it off. After that, you apply a lite coat of primer for the paint to adhere to.

I also use the West Marine epoxy resin. It has a pump system so you get the same mixture evertime. Ther also sell a fast and slow cure hardner. I use the slow cure. It gives you about 45 minutes of working time.