No special adapters needed for the pressure tank?
Can you get heating elements that will screw into those standard threads?
(If you wanted to use one).
I like the looks of the pressure tank. It appears to be heavy duty hardware.
If you seal up the exterior paint job real well before insulating, that thing might last a life time.
The tank could be insulated a few difference ways, and it shouldn't be too hard to DIY and get a good low loss tank.
The exterior of the insulation doesn't really need to have a sheet metal jacket.
But, some bright metal foil in layers to reflect IR might be a good idea.
I say, Go for It!