Hello Dan, welcome to allmetalshaping. I have several threads on here showing aluminium coachbuilding. In my opinion. Being able to gas weld the aluminium is key. I show some of the process on my youtube footage. Here are some links to some threads showing aluminium coachbuilding.
http://www.allmetalshaping.com/showthread.php?t=9410
http://www.allmetalshaping.com/showthread.php?t=1468
http://www.allmetalshaping.com/showthread.php?t=1096