I think he ones I've seen locally are purpose built warehouse type set ups. A growing industry, probably unsurprising for us to hear that. The shipping containers I'd forgot about. That set ups been around a while. A friend loosely runs a business from his! With business in mind it does make justifying easier.
Ross, I did have an affordable garage, I'm losing it soon though, plus its a bit damp, plus the dopey daughter of landlord left it unlocked and ultimately wide open for a week so after loosing 8 alloy wheels I've gone off garages, though if I found another cheap I'd sling a car in. Dehumidifier is a top idea, TBH if I got a container cheap it'd be ace! The purpose built places near me basically offer a small broom cupboard for £26 pm. That would mount up long term, yeah.
Boat show, and caravans, clever stuff. That's another plan!
Shed? You cold call it that!