Does anyone have any tips for painting the aluminum housings on the trans and diff? Is POR-15 the way to go, even though it's aluminum?

I'd like to paint them, and have time before my kit is delivered. I haven't decided between black, silver, or red - but definitely would like to do it. I'm concerned about adhesion and durability.

If anyone has any experiences with POR-15 or other coatings for these applications, please let me know.

Thank you,
--Curt