A spool gun for Aluminum is great for aluminum sheet work where you need to utilize speed. I recently sold my Spool gun for my Miller that i used to Fab cabins on boats in the late 80's early 90's. It made quick work of short stich welds and inside corners on .100 & .125 sheet. But on the outside rubrail we used our old Heliarc machine to get a nice looking clean strong weld. Any fuel or oil tanks we built were done with the old Heliarc machine also as you can produce a better seal on the outside corners. As mentioned in another post here Tig will also give you the ability to add some cleaning for the old dirty and oily parts.
PowerTig 200DX
Supercut 50P
PowerTig Micro 185 SOLD GREAT MACHINE
Millermatic 200
Miller Thunderbolt
Jet 1340 Lathe
Jet 20" Drill Press
Jet 12" Wet Band Saw
Kalamazoo H7 Bandsaw
Forward 12,000 lb 4 Post Lift