Tire Chains are not all that useful for a cross-country interstate trip. If conditions on the interstates are so bad that he'd need chains to get by, then he really has no business being on the roads at all. He should find a comfortable place to stop, and let the plow crews do their thing.

Sleeping in a car at a truck stop isn't dangerous from a crime type perspective, but doing it in February? It could be quite dangerous from a hypothermia standpoint! Other than blocking the wind, a car provides almost no insulation from the elements, and trying to stay warm by using the cars heater while sleeping can be deadly due to carbon monoxide. Unless he has heavy duty winter camping gear, I wouldn't recommend it!