Well, as long as you don't get out of your vehicle while you drive through PA, you can carry in on you in your vehicle. However, stop and get out with your firearm and you'll be breaking the law;
6106. Firearms not to be carried without a license.
(a) Offense defined.--
(1) Except as provided in paragraph (2), any person who carries a firearm in any vehicle or any person who carries a firearm concealed on or about his person, except in his place of abode or fixed place of business, without a valid and lawfully issued license under this chapter commits a felony of the third degree.
(2) A person who is otherwise eligible to possess a valid license under this chapter but carries a firearm in any vehicle or any person who carries a firearm concealed on or about his person, except in his place of abode or fixed place of business, without a valid and lawfully issued license and has not committed any other criminal violation commits a misdemeanor of the first degree.
(b) Exceptions.--The provisions of subsection (a) shall not apply to:
(11) Any person while carrying a firearm in any vehicle, which person possesses a valid and lawfully issued license for that firearm which has been issued under the laws of the United States or any other state.
Also, while firearm and ammo must be carried in seperate containers, there is no requirement that they be locked or carried in the trunk.
"The Marines I have seen around the world have, the cleanest bodies, the filthiest minds, the highest morale, and the lowest morals of any group of animals I have ever seen. Thank God for the United States Marine Corps. Eleanor Roosevelt, 1945"