Back when I worked with car audio installations, I would use combinations of sanding, bondo, sanding, cat hair for the thin spots, sanding, feather fill for any grooves or scratches, sanding, sweating, primer, sanding to make dips visible, bondo, sanding, etc. Feather fill was awesome for filling in sanded scratch marks. Are there any small volume products available to the "model" world similar in function and effect? Possibly closer to equal mix ratios as well? A 10:1 ratio would be less than an eye dropper at the amount I would be mixing at a time. I've been "watering" down clay to press or brush in, but it seems that gets more on my hands or the brush than actually sticking in the grooves.