A car is not suitable for more than a couple of nights emergency accommodation.
He will find it more comfortable, practical and warmer living in a tent.
If he is thinking long term then he needs a van, one you can stand up in.
It needs to be insulated and it needs some sort of heating and cooking system
However once he taps into the "FLT" * network, there are places to stay, which if they are public, you need to move on after a couple of nights.
It's not a particularly cheap way to live, and it's not an easy life.
Quite frankly, his best option would be to get a caravan and park up in a mates drive or back garden.
I had a mate who as a student living is a shared student house in Oxford, they had a guy doing PHD who lived in a caravan at the end of the garden, he had been there for at least 3 years and paid whomever the current residents were that year a small amount to use the loo/shower by the back door.
(* FLT = Freedom Loving Traveller/Free Loading Tosser depending on context and your point of view)