The only thing more difficult to TIG weld than aluminum is copper. Both materials conduct heat away from the weld area so fast that a huge amount of current must be available to get a good weld. The best aluminum welding I've seen has been done with a water cooled TIG torch, a foot pedal current control, and a high frequency starting arc. Do the small portable machines have the high frequency starting arc available? If not, don't even consider one of them if you're trying to weld material much thicker than a Budweiser can!
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!