First, give your friend a dope slap for moving to a new state and not checking the handgun laws first. Then another for assuming that he can carry in his car. In some states, like NY, just owning a handgun requires a permit. You cannot move there and take your handguns with you because you have to be a resident for at least 6 months before applying. If you get caught with them you do not pass Start, you go directly to jail and pay through the nose.
You need to have permit to have a loaded firearm in the car in TN. Since TN issues CCW permits your friend should just go pay the $115 and get one. It's a shall issue state so if he meets the requirements he'll have no problem.
He also gets pretty good reciprocity, see the "Who honors my permit" link at .http://www.handgunlaw.us/
There is some info on some recent changes (they made them better) to their CCW laws if you scroll down at http://www.state.tn.us/safety/handgun/handguntca.htm
39-17-1307. Unlawful carrying or possession of a weapon. —
(a) (1) A person commits an offense who carries with the intent to go armed a firearm, a knife with a blade length exceeding four inches (4²), or a club.
(2) (A) The first violation of subdivision (a)(1) is a Class C misdemeanor, and, in addition to possible imprisonment as provided by law, may be punished by a fine not to exceed five hundred dollars ($500).
(B) A second or subsequent violation of subdivision (a)(1) is a Class B misdemeanor.