For painting your aluminum I have used a product called SEM with good results. Here is a link
https://www.amazon.com/SEM-39673-Bla...etching+primer
Most cars have plastic bits now and I'm pretty sure that the painters use some type of flex agent mixed in with the paint, so the paint does not peel off.
You could try your local body shop supply house for your supplies.
Another thought is go to the local body shop and maybe the painter is willing to help you out.