>>10248482 You don't go from 400 to 2000 immediately after if you want to get rid of nub marks and scratch lines.I have a very simple process for this if you want to spend the extra time cleaning up nubs, mold lines, and scratches. It consists of going up in grits by 400/500 and sanding perpendicular to the last grit you used in order to keep scratches from staying there.
Start with 400 and sand lightly going, say, up and down.
Then, when you're satisfied with the mold lines not being there, go up to 800 and go from side to side.
After that, use a higher grit between 1000-1200 and sand up and down once more.
Keep this Sequence of The Sands going until you're happy with the end results: a seamless surface that doesn't have a nub mark or mold line in sight.
Oh, and if you're worried about dust getting everywhere, get a cup of water and wet your sanding tools. Particulates dont go anywhere when it's damp, and once it begins to dry, just apply more water. Plastic doesn't care about water, afterall