rmssetc
Contributor
I do not have any personal experience with these bags but I know Marissa (Hidden Worlds Mexico) was selling them at one point. They can hold 2 Al80s. I've seen some people use them.
KUBI S80 Twin Cylinder Transport Bag (KUBI-2xS80)
www.kubistore.com
If I absolutely had to carry 2+ tanks & gear on my back, I'd look at a haul bag, designed to, um, haul 100+ lbs of gear while rock climbing, designed with abrasion resistance and lots of strong attachment points.