Building a room from copper RF shielding panels [1] and soldering them together is a lot easier in the field than supplying a whole liquid helium or nitrogen cooling system. The former is well within the capabilities of a forward operating base - they can just ship the shielding in on plywood and the electrical technicians are more than capable of soldering copper.

[1] https://www.nelcoworldwide.com/medical-shielding-products/rf...