Since I got it assembled, I learned the actually size so I made a floor to mount it onto. Some scrap stock glued up and some polymeric resin casting stone scraps that I glued to the sides and cut to width with the bandsaw - nasty stuff and well worth running the shop vac.
Some 1/16" thick scribed siding for the floor - marks are where screws from underneath will secure the structure if/when an interior is installed.
In a time like ours seemings and portents signify. Ours is a generation when dogs howl and the skin crawls on the skull with its beast's foreboding.