WWII brought jobs, and those temporary homes were a product of that as jobs were springing up everywhere. What happens if there are no jobs...there won’t be a need for places to live, but food will be a necessity during famines and no income.
The three minimum things that even a devastated federal government can do is provide housing, which they have, and provide food, which to a great extent they control, and to keep order.
But this is a bare minimum. The individual States can contribute by producing scrip currency (CA and KS are doing this right now, in a basic way). This keeps State and local government, and commerce flowing, even if the national currency has become unstable.
This gives an opening for small scale producers and entrepreneurs to get the market functioning again. And small business employs more people than big business, so it starts to build momentum.
Many jobs just have their pay downgraded to local levels, such as doctors, school teachers, policemen, firemen, etc. They don’t ever face unemployment, because they can’t, even if they work for room and board.