I've seen people adapt aluminium horizintal-mount forklift
tanks, some for both vapour and liquid service. Not expensive second-hand.
Available in 33.5 and 43.5# sizes, can be fitted for
remote fill in place rather than removing.
But obviously adapters are needed for the various locations.
Hard to get qualified techs to help with such shenanigans in "well regulated" jurisdictions, but it's not rocket science and quality
parts are easily obtained once you know the terminology.