Well what I did was apply it directly to the paint. I'm just totally experimenting but so far the results have been amazing. I did encounter some problems applying the dust effects...it mixed with the engine metal pigment. So I just clear coated the model with rust-o-leum matte spray and I'll try the dust again with a cleaner surface. Then I'll dull-cote the entire model.

This forum rocks, I've learned so much from reading here!