Just my limited but relevant experience around anodising in a marine environment.
Both my junk rigs have had aluminium tubing sail battens. I couldn't find already anodised tubing. For Cadenza first time round, I found a place (in North Manchester) which anodised the tubes I bought and took to them. It took a week, and cost about three times what I paid for the tubes.
Second time round, for Cavatina, I researched (on line obviously, but I can't remember how/where), and discovered an alternative method, involving careful cleaning and then the application (with a brush) of two different chemicals consecutively. It seems to have worked well: 5 years later the battens are absolutely fine. They do get salt spray, and an occasional dunking in sea water.
I suppose anodising reaches the inner surfaces of tubes: I couldn't with my other system, but as the ends of the battens are plugged, this doesn't seem to matter for my application. I have found absolutely no visible signs of corrosion, and I doubt that they are being eaten from the inside.
I recall that chasing down the relevant materials involved websites supplying people who build their own aircraft. It involved a bit of DIY faff, but worked out a whole lot cheaper than anodising. So if you get something smallish made for you in aluminium, there are alternative methods of marine protection.
Michael
