third gen formula style rear hatch spoiler

I own a 1989 formula with a rubber spoiler. I am going to paint the car. I need some advice on how to prep this piece for painting. can anybody help?

with it being rubber, it is an issue.

you can do it like nromal, but any flex will cause cracks or chips. i guy here in town fiberglassed his for strength. it has the same shape but was better.