Crators in Acrylic paint job

I'm painting my HD F-150 for the 4th time. I use Testors MM and I can't paint the gloss black without getting these "crators" in the paint on the body of the truck. It gets humid here so I wait for a low day and I do all the pressure, thin the paint,moisture trap and all that. Anybody?
Thanks.
K.

Source: http://cs.scaleautomag.com/SCACS/forums/thread/975541.aspx

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