Man I'm sorry I don't know how to weld aluminum but I don't see why everybody is telling you to pay for it to be done. These guys sound like my Dad, if I listened to him I'd never have learned how to cut, weld, fabricate, paint or anything. He is a "you can't do it if you don't know how" guy. I say nonsense. You have the spool gun, filler and something that needs welding I say get 'er done. It's just a boat, not the space shuttle.
I needed an aluminum oil pan welded this week and took it to a boat fabricator, they were nice folks, bet they would be more than happy to show me how to do it but if I had the equipment I'd learn to do it myself. My motto is "A man can do anything with the right tools".
You might find some info here:
http://www.millerwelds.com/resources...rticles10.html
www.weldtalk.com
Hope this helps!