If you're going on a roadtrip, I recommend checking out
CouchSurfing
Sleeping in one's car CAN be a little sketchy. Enforcement and danger varies by the area. Over the summer doing door to door sales in California I became skilled at taking naps most anywhere. One may be better off finding a place to park and then go off somewhere less visible. If there are many trees with few people around at night, a tent hammock could be lovely (and more comfortable than a car seat anyhow). You can use them in areas that may be too rocky or wet for tents, and they can be set up or taken down in a couple minutes. I haven't yet tried this myself, but it looks promising.
HENNESSY HAMMOCKS: ultra-light line of jungle hammocks, ultra-comfortable camping hammock /chair/ tent combo