Getting anything to stick to aluminum long-term can be a bit of a chore. I held off posting because I have only limited experience. I used to have West System instructions that suggested sanding the wet epoxy into the aluminum (thus the epoxy can bind to fresh aluminum before a new oxide layer forms). I've done some tests of this and it seems to work well. Otherwise you need to use something like alodine to prep the aluminum. If you don't remove the aluminum oxide before you start applying anything (with the exception of sanding wet epoxy) you are going to have trouble with paint peeling and bubbling off the aluminum.
It might we worth trying to sand/smooth one end of the tube as an experiment. You might not have to remove much material to smooth the mast out. Sanding and polishing the aluminum would likely be about as much work as painting, but would be longer lasting.
My $0.02
Darren