Using a rubber sanding block and 150-grit, we sanded the paint and rust from between the ribs of the trunk floorpan and to feather the edges of the areas where we used the 36-grit and the angle grinder. We used dry paper instead of wet for this job. The rule of thumb is to use dry paper for feathering edges, taking down filler, or sanding primer. Use wet paper for jobs that require grit over 320 like when you are prepping for paint. When using water, the finer grits are less likely to clog, and any debris that might scratch the finish is washed away.