I just wanted to throw in my two cents...
I painted a plexiglass marquee in a similar manner. I masked off the inside section with Painter's Tape, and sprayed the outside. While the paint looked fine, the painter's tape did not create a clean edge, and I had a few moments of panic and swearing. In the end, I used ammonium (nail-polish remover) and some Q-Tips to clean up the edge and it now looks good. Just keep this in mind when you are masking, and try to make sure the paint won't get under the tape.