Confederation Marine Modellers
From Bob I: As many know I'm big on sanding, filling, resanding and repeat again and again. I use finishing bondo in the tube that I get from Canadian Tire in the Automotive paint section. I like it as it's very fine for small holes. I use plastic oil painting knives from Michaels. They come in a package of a few different sizes & blades and are not expensive at all to apply the bondo. Applying thin layers are better than thick as it dries very fast and can be faster with a hair dryer. Also, when finished sanding it takes paint very well.
The most important trick I've learned about sanding is to wipe the surface frequently with a soft micro cloth, then I'll close my eyes when I'm feeling the surface for deficiencies as your eyes will fool you but your touch won't.