Only in Nebraska....
I remember a police report a few years ago in the North Platte paper. A couple had been, um, enjoying some recreation on the hood of their car after undressing inside the car. Afterward, they realized that the keys were inside the car and the doors had locked. The state patrol found them, and either jimmied the car or got a locksmith out. As I recall, they didn't even ticket them. 
I would like to know if driving naked is illegal in New Hampshire long as the driver is sober.
People do expect privacy in their enclosed cars, sort of like being in their homes.
It at one time amazed me the number of people that like to live in the buff, especially when there were children around. All these Nudest Colony's with naked folk froliking about bare as a jay bird and their kids, from 2-17+ wandering about. This does not sound healthy to me as who knows who has been sitting on a chair before a kid jumps up on it. Just sanitation alone is a question.
Then the question of sex comes in as children have been raped and the parents do not report it fearing loss of the child to CDC.
However back to the topic, as long as someone is wearing their seat belt and shoes, in a enclosed truck, van or car, what is the laws on how they should dress????