Hi James,
Disclaimer first - I have never done this!

However, as Rustoleum is an oil-based enamel, plain old Paint Thinner, aka Mineral Spirits, would be the thinner-of-choice, but I don't believe you can thin the stuff enough to get it through an airbrush! I Googled the topics, and they were talking about 10:1 thinner-to-paint and using conventional spray guns. For a 40 psi airbrush, you might have to go to 50:1.

Have you tried Brodak colors? I just tried an experiment with the Silver. I combined 1 oz. Silver, 3 oz. Clear and 3oz. Thinner, almost water thin, and got complete coverage in 2 coats on a solid surface! Sutface prep was 2 coaats of thinned clear, Jap Tissue applied with thinner, and two more thinned coats of clear. Then the color as described. Best-looking Silver I've ever done.

I have thinned canned Rustoleum and sprayed it with an airbrush to paint the canopy on a profile. Used acetone for thinner, worked well for the small area I painted but not sure I would try to do a large area with an air brush.

Have no idea what I ended up with as far as how much thinner to paint, I mixed very small amounts and just added acetone till it looked about right, did a test spray and added more if needed... Not even sure acetone is the correct thinner but it worked.

Could have it mixed up with another product but seem to remember the can saying to use Rustoleum thinner which I didn't have so just tried acetone and it worked..

I have thought about taking canned Rustoleum enamel, thinning it and brushing it on like dope.  Would this work?  Glen

Yes.  I painted a profile with white Rustolem rattle can before assembly.  I touched up the wing to fuse and fuse to tail joints with rustoleum from the can with a brush after assembly.    It is real thick, and takes a lot of thinner.   I have brushed it on to fix repairs too.