Try a plastic barrel for the GWHX
I tried a plastic barrel that I bought earlier for garage thermal mass.
It has a removable top of about 15 inches in diameter -- maybe enough to get the pipe coils into? The top has screw threads around the 15 inch dia, and a gasket -- see pics.
Overall height = 42 inches
Max diameter = 23.5 inches
The standpipe goes up 57 inches above top of barrel.
The lid had a removable plug in the center that matches the 2" PVC pipe thread fittings -- I took this out, and installed the standpipe so the drum could be tested for leaks with a little pressure.
I bought this barrel used from the local Ag supply place for $30. As I recall they had a similar one that was shorter -- which might be better.
The barrel started leaking slowly when the standpipe was filled with water (about 2psi). I tried tightening the lid with a block of wood and hammer. This slowed the leaks down more, but did not stop them. It also looks like the barrel lid bulges out a bit -- this may not be a problem. Not sure if maybe a new gasket, or some type of supplementary sealer might help?
If the steel barrel seals well, then maybe its the best deal -- I just thought that I had the plastic barrel on hand, so why not give it a try?
The Ag store sells a lot of new Ag related poly containers -- from a few gallons up to more than an thousand gallons -- lots of shapes and sizes. I strolled through them, and did not see anything that was just right, but the manufactures would have more. The prices were fairly reasonable, but nothing like the 15 bucks a barrel or used steel barrels.
Just some more data to think about.
Inside of lid showing gasket
Barrel and standpipe
Left pic shows slow leaks -- Right shows slight bulging of the barrel lid under pressure.