I should add a followup about the automotive primers. I used Rustoleum, and WalMart's house brand. They worked well as primers, though they're a little coarser than Tamiya's.
I stopped using them because of a mechanical problem-both brands changed the type of nozzle on their cans, and I found that the nozzle and the opening on the can clogged consistently. The nozzle can be soaked, but the opening at the neck of the can couldn't.
Apparently, though, Rustoleum has changed the type of nozzle again, and I may buy a can to see if the new type eliminates the issue.