[Wavytone]

There’s another solution.

There are companies that manufacture “site sheds” for construction companies - to your design - using walls consisting of a sandwich of 50mm polystyrene between two thin aluminium skins.

They can make these with a door and or windows where desired and they include channels for wiring pre-set in the plastic, a light, switch and a power point or two included; all you need then is to connect it to whatever power you have - 12VDC being the easiest as you won’t need a sparky for that.

I’ve used these to house industrial instrumentation requiring precise temp control inside in remote locations and I can say the thermal performance was excellent particularly if the exterior colour was white. Interior temps were very stable and no condensation inside.

Can be made in quite small sizes suitable for an obs the size of a 6 x 4 trailer or garden shed - I have also seen these on trailers as enclosures for portable toilets.

Only thing to note is that all metal sheds conduct electricity extremely well so think about the risks of short circuits (fire - with 12VDC batteries) or electric shock (240VAC).

Sure one of these will cost a tad more than a Bunnings garden shed but less than the gear inside.

Also you could consider an unusual design eg one with low walls to take a roof that opens like a clamshell.