http://www.handgunlaw.us/states/pennsylvania.pdf
The way I read it, you can open carry outside your vehicle in PA without a license, except in Philadelphia. Inside a vehicle it looks like the firearm must be unloaded and in a locked exterior compartment of the vehicle or in a locked case.
Also, you probably want to be mindful of this definition of loaded in PA law:
"Loaded." A firearm is loaded if the firing chamber, the
nondetachable magazine or, in the case of a revolver, any of
the chambers of the cylinder contain ammunition capable of being
fired. In the case of a firearm which utilizes a detachable
magazine, the term shall mean a magazine suitable for use in
said firearm which magazine contains such ammunition and has
been inserted in the firearm or is in the same container or,
where the container has multiple compartments, the same
compartment thereof as the firearm. If the magazine is inserted
into a pouch, holder, holster or other protective device that
provides for a complete and secure enclosure of the ammunition,
then the pouch, holder, holster or other protective device shall
be deemed to be a separate compartment.