I gave up (at least for a little while) on the Mr. Surfacer, and instead took a bottle of the Tamiya primer (I used the white, but grey is fine too) and decanted it to spray with the airbrush. It worked perfectly. I have just had too many problems with the Mr. Surfacer, but many people use it and don't have any problems at all! Just my luck, I guess. I've tried just spraying out of the can before (at least with Tamiya primer, but not with Mr. Surfacer) but they always put out way too much product for me and lay it on too thick. Once decanted, however, it sprayed on awesome through the brush. So I'll probably stick with that for the near future.
And yes, no need to sand after applying the Mr. surfacer 1000 and 1200. Lays down a nice, even, flat coat (when it isn't turning into spider webs!). Anyone out there have a solution?
Jon