Complex sentence: Personnel at the remote sites lived under the snow in metal structures connected by unheated hallways of steel corrugated tubes and when they did go outside it was though hatches in the ceilings to access axillary structures and the radar antennas.
Split into simpler sentences: Personnel at the remote sites lived under the snow in metal structures connected by unheated hallways of steel corrugated tubes. When they did go outside it was through hatches in the ceilings to access auxiliary structures and the radar antennas.