Housing crisis solved?

I think that given the extortionate price of property in London and  the south there was an obvious solution.
Anyone who has used a modern touring touring caravan knows how packed they are with all the mod cons for a couple in space barely 2x5metres. So why not use this technology to create affordable homes for homeless and single people or couples who want a compact home and spend a lot of time ofut?
You could build these in buildings like rooms in a hotel. Door inside in a corridor and a window out side where the front of the "van" would be. £20k each!