Duraglas is hard to sand and I use it on the low spots and edges, then use Evercoat mud over that and then glaze if needed.
1st coat I sand with 36 grit then go to 80 and then 180. If you let the bondo dry to long on the first layer it gets to hard to sand. Let it get almost dry then hit it with 36 grit. If it's still to green it will gum up the sand paper and not be able to clean it out to easy.
Makes a big difference in wearing out sand paper and arms.