OtterSC Customs has something on spray painting your marker here.
It states that you should use a few coats of Krylon, Rustoleum, or any other outdoor based paint on top of a few layers of a good primer. Read the whole article and follow the steps to get the best out of the painting. Unfortunately, I haven't done this process before, but it seems that the paint would hold up very well.
Hope I was some help.