The mirror will be on tomorrow because I actually had a couple of days that were warm enough to spray paint. Here's how it ended up looking:
It is rough, but not as rough as it was. I used a wire brush on the rust before I sprayed anything. It is also gonna be covered by the actual mirror housing so it doesn't matter that the color isn't quite right or that it isn't exactly smooth. (paint also needs to dry and i'm no good at spray painting in general so i'm happy with how it looks right now.)