Ah. I didn't put enough significance on the 'bunker' part. How about finding a property on top of a cavern? I've come across at least one. Or a missile silo..

Bus could be electric, or CNG, or E85, hydrogen, or B100 powered. I once met a guy at a remote intersection in Nevada who was driving a 40ft skoolie back from deep in Mexico to the PNW on collected WVO.. part of an annual migration.