One of the problems of underground home construction in general is that additional humidity settles into the lower cavity. Thus underground home builders favor areas in the midwest which are by climate typically more arid. The additional humidity is uncomfortable and causes things to corrode faster. Also, when steel is underground, it sweats, fiberglass does not, so any air space between your inner steel wall and the insulation however small it might be, will be damp, inviting corrosion, mold, bacteria, maybe even shorting out electrical connections depending on the setup. The only way around this that I can see is to use the much more expensive foam-type insulation which will adhere directly to the wall itself. An above ground or partial-bury can be ventilated much more easily, without the use of blowers and fans which can break and need a constant power source. Heavy gas collection is also a concern, i.e. Radon (radioactive carcinogen) carbon dioxide, propane, maybe more.
Offered by Steve.