Over the past few weeks, he has gone from lying down in the back of my Jeep to barking like a nut at every person, beast, or vehicle he sees. He sounds like he wants to kill everyone.
This (or having people in your house) don't necessarily indicate bad nerves.
It can indicate that the pup needs more exercise as he's grown bored and is noticing things more.
Dogs, when bored, make up "games" and your dog's current game is "oh look, intruders!"
Gently discourage, and crate while in the vehicle.
And exercise the puppy more, especially before going places.