Dan
Since you're in AZ most of the problem will be that the paint needs to expand and contract as the metal will.
While I've had good luck with plain old model paints (Testor's, Model Master, Pactra), it's also because I'm up here in the PacNW which tends to be much gentler on temperature spikes and dips.
However, with that being said, one type of paint that I've used is the Pactra line for R/C Plastic bodies. These bodies get painted from the underside, and since the plastic body is very flexible, the paint needs to be somewhat pliant and bendable. It will eventually crack (especially if the body gets flexed a lot) but should last longer than a dry-hard paint such as the other model paints. The only thing I am not familiar with is how well they'll fare in the high temp extremes you guys can get. Look for it in your local Hobby Shop and ask them for piant for clear Lexan Bodies (R/C Cars & Trucks), you'll find all sorts of colors. Be sure to pick up the brand specific thinner, as other thinners and solvents will just curdle the paint.
But that aside, the biggest obstacle to getting paint to stick is to ensure that the surface you're painting is CLEAN. I don't just mean free from dirt, I also mean wax and grease free. So, put those emblems in the sink, use plenty of warm/hot water and scrub the heck out of them with a toothbrush and some grease cutting detergent/dishwashing liquid. I use Dawn and it cuts through some awful gunk easily.
Afterwards, blow dry completely and then use some of the thinner for the paint to scrub the surface to be painted. Wipe / blow dry and allow to sit for a minute or two (to let the excess solvent evaporate). Then paint to your liking.
Hope this helps.
Enrique
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