If it was me I would remove the paint on the external housing and leave it as bare aluminium. It does not need paint to stop corrosion. With the amount of disimilar metal around getting any paint to stick is going to challenge.
If you do paint it you need to follow the guidelines to the letter.
International would recommend 5 coats of epoxy
interprotect then 2 coats of undercoat then 3 coats of perfection.
Other pain system require a different procedure often with an etch primer.
Power coating does not work
Anodising is another option with a small part like this. You can even do this youself with smallish pieces.
Wherever you have SS bolts going through aluminium you need to protect the aluminium with a product like Duralac.
The main weapon against the disimilar metal corrosion with the internal parts
is to keep the components dry. Easier said than done, but at least try.
Spraying the internal components with one of the car cavity wax corrosion protectors is worth doing.