In teaching people to GTAW weld I've only had one guy who only wanted to do aluminum and took to it right away. Everyone else struggled. AL takes a different mental approach than does ferrous metals.With a GTAW I've found that thin AL works best on DC-Reverse Polarity. Thick stuff, like cylinder heads, needs what I call "back-ground" heat. AL dissipates heat fast enough that it takes a lot of power to weld. By adding some back-ground heat to the part it slows the dissipation rate. On a camper frame I'd expect to only need back-ground heat on the heavier sections if the machine has enough power. the shorter on power that the machine is, the more pre-heating will need to be done. With GTAW using helium on AL reduces the power requirement by about 1/3. I've not tried it using GMAW on AL because I've done very, very little GMAW welding of AL.
In the town that I went to college in there was a boat builder who built Rogue River type AL hulls and they used spool guns exclusively. There is merit to this, the liner in a traditional GMAW system should be changed to an AL exclusive liner when running AL wire. For whatever reason the liners don't seem to last as long with AL running thru them. A spool gun removes all of that from consideration.