Lithium battery container

[mudski]

Everyone's pretty well covered it, but I'll chuck my 2cents in.
I'd go a small concrete slab and brick/block bunding for a couple of courses, then light timber or steel frame. Can double-skin it with corrugate (cladding and lining) and fill wall with whatever insulation. expol, glass batts, foam, hemp, whatever.

I do this but a full course of brick all the way up, double brick would be even better for insulation reasons, and a steel frame for the roof and then insulate the roof. I wouldn't use timber at all if I were to do it.