Welding Aluminum with a MIG is fun, but if you're doing anything thicker than 1/8" you need a bigger welder.
Why? Because aluminum is a big heat sink. The arc is what creates the heat needed to melt the metal. With aluminum, it dissipates the heat so quickly that you need more arc voltage (with MIG) to melt the metal than you would if you was welding mild steel.
Lot of guys say it can't be MIG'd, but it sure can. I've built many projects with an old Lincoln Weld-Pak 100, with a spool of aluminum wire and 100% Argon. 99% of the time the voltage was turned ALL the way up, as was the wire speed.
With Aluminum, it's sorta backwards. Generally speaking if you're burning holes, you're going too slow and need more heat. Sounds odd but that's been my experience. TIG is a little different obviously, but same principles apply...especially with heat needed. 200A TIG unit will be max'd out with 1/4" aluminum and I mean MAX'd out pedal to the metal and feed plenty of filler as fast as possible.
Clean clean clean! Aluminun needs to have EVERY ounce of clean put on it. Why? Aluminum oxidizes quickly (that's the white stuff you see on Al that's been sitting outside for a while). The oxidation...Aluminum Oxide...melts at around 3700 degrees F. The aluminum itself melts at around 1200 degrees. See a problem? Then dirt...grime, grease, etc...all will adversely affect the quality of the weld. The weld in the picture above has a little junk in it, but otherwise looks pretty good. Better than I can do but I'm no pro..FAR from it. My eyes are getting worse and that's affecting my welding skills severely. When I say clean, I mean clean the contact tip (or tungsten if using TIG), clean the filler material (wire/filler rod), clean the base metal, clean all metal to be welded, and everything within 1 inch of the weld. I even clean the table I'm welding on because I've had instances where something was on the table and spattered into the puddle while welding. That's always fun to figure out. If you use a wire brush, use a known clean one made specifically for cleaning aluminum, and use it for NOTHING else until you're done welding. IF TIG, grind your tungsten on a wheel that's fresh and will not be used for anything else but grinding aluminum welding specific tungsten as if you grind something else, it gets embedded into the rock and will make its' way to the tungsten-contaminating the puddle, and throwing you for a loop. Fun stuff. You'll get good if you do it enough.
The jet jon idea has me intrigued, big time. I want to watch some of these threads. Used up/wrecked jet ski's are everywhere out here, and dirt cheap.