That's the first thing that came to mind when I read that, is that the air brush just doesn't produce enough material to get a nice coating that is even. I bought a Blue point/Badger DA airbrush about 25 years ago along with a Binks diaphragm compressor for painting models that I have never used to this day ( I was always afraid of messing it up not knowing how to use it). I really want to paint my Dawes myself and I have a line on some free laquer paint and someone who knows how to paint with it that will let me use his detail gun and give me some pointers. The only guns I own are full size and require to much paint to be mixed to get them to flow right without the fear of running out in mid stream. The prep work is what has kept me from doing it before as I have problems with my hands and sanding hurts, but now I have a bead blast cabinet to help me strip the old finish off but I still feel that it would be best to skim coat that entire frame with a filler like they do when painting a car. Is any of this any better then if I were to do as the OP wanted to do and brush it on and sand between coats ( I can get my nephew to sand for me) or do I not need as much prep as If I were painting a car.

Glenn