You Tube blogger 007craft has done just that in the USA —in a U-Haul storage unit. The key, he says, is to do nothing that could get you noticed.
I had just came back from hiking the Pacific Crest Trail and found myself homeless. I had given up my apartment to go hike and now that I was back I wanted to turn my car into a livable space. I eventually did that (follow this link to view the video) but found I still needed access to lots of stuff from my storage unit which was 6x4x10 and everything was just jammed in there. I figured there had to be a better way. I scoped out a 10x10x6 unit and moved all my stuff inside. Still super small, I managed to build shelves and organize it in a way where everything is accessible. But why stop there! I decided to build shelves and a water system and setup my actual apartment so I could live there. I was moving in! I ended up living in the unit for around 2 months.
The cost of rent on the U-Haul unit was $205 a month (which included insurance). A bargain, considering an apartment in the area was $1000+ a month. He made this video showcasing his work/unit.