Hi,
Jay has it right, people can only see what is at eye level anyway. I did mine (Le Fiell Tabernacle Mast/W32) a few years ago by sanding the mast by hand and painting it. Sandblasting with what ever blasting media, tends to add tensions to the surface of the mast extrusion. Being in a business where machining thin walled parts improperly causes the parts to come out distorted, the same with masts. There is no magic that sandblasting will substitute for a decent primer.
I looked this year at the entire WOA comment web site to find inspiration for myself and also I hope that I will not offend others by my criticism. I may not be 100% correct, but I have been more correct than wrong (so far). I am adding this because there are lots of opportunities to educate oneself so that some hungry yard operator (wolf) will not eat your budget and you end up with a second rate job.
Fair winds,
Mike Z