When I'm welding alum I use lots of clamps for heat sinks and I always clamp to a backing so the puddle won't fall through. Just a hobby guy.
My tungsten stays shinny using 15 CFH. (1993 250 Syncrowave, air cooled torch)
This is thicker (1/8") so I don't have the larger backing I'd use for the thinner guages. I'd also have backing behind the corners.