I "live" out of my car for up to 2 weeks at a time during my summer travels; it's much, much cheaper than using hotels, I get to see interesting places, and there's a feeling of freedom travelling that way when you aren't tied down to a fixed physical location.
I don't bother with cooking; I just eat cold food on the road, like yogurt, fruit, vegetables, sandwiches, etc. Shower at truck stops ($10-12 for a shower, and national chains like Pilot are always impeccably clean) or, now, I have a Planet Fitness Black card so I can go to any PF nationwide and shower.
Finding a place to park is the hardest part. I like to use Walmarts--3/4 of them allow overnight parking (google "no park walmart")--or campgrounds. I've never tried stealthing it on the street; that seems like inviting hassle from the police if you're discovered.
One of my projects over winter break is to add some thermal insulation to the cabin to make it more comfortable to sleep in, and revising my window blocks. They're currently just Reflectix cut to fit the windows, so I'm going to back them with 1" XPS board (R-5.0). In the doors and behind interior panels I'm fitting 1.6" denim insulation (R-6.7) and Reflectix radiant barrier. This should slow the rate of heat transfer at least a little--better than what's there, which is nothing.
The first year I camped this way, I took along a cooler, but last year I bought a 12V cooler/heater. Much easier; I don't have to bother with buying ice and draining water. The Prius' 12V socket will run up to 10 amps, more than enough to run the cooler and charge my cell phone and laptop with a little 100W inverter plugged into it.
(Glacier, 2016)