I saw a truck cap offered for free on Craigslist and not having a truck, my mind went elsewhere.
With a fiberglass exterior and aluminum bones, it seemed like a structure that could survive direct burial or at least survive contact with the soil.
There are a lot of examples of these caps being used as shed roofs, I propose doing the same, but building the shed over a shallow trench, and earth berming the roof and three of the sides.
Accommodations could be made to allow light in through the windows, or they could be covered up entirely.
An example of a truck cap shed from hackaday.