Here is the chapter and verse regarding the applicable federal law, I think it was passed in the 80's - I don't think any state between PA and Co would be any problem anyway though, if they were in the trunk of the car or in a cargo compartment of a truck, except Illinois.
http://caselaw.lp.findlaw.com/casecode/uscodes/18/parts/i/chapters/44/sections/section_926a.html
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United States Code
TITLE 18 - CRIMES AND CRIMINAL PROCEDURE
PART I - CRIMES
CHAPTER 44 - FIREARMS
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U.S. Code as of: 01/22/02
Section 926A. Interstate transportation of firearms
Notwithstanding any other provision of any law or any rule or
regulation of a State or any political subdivision thereof, any
person who is not otherwise prohibited by this chapter from
transporting, shipping, or receiving a firearm shall be entitled to
transport a firearm for any lawful purpose
from any place where he
may lawfully possess and carry such firearm to any other place
where he may lawfully possess and carry such firearm if, during
such transportation the firearm is unloaded, and neither the
firearm nor any ammunition being transported is readily accessible
or is directly accessible from the passenger compartment of such
transporting vehicle: Provided, That in the case of a vehicle
without a compartment separate from the driver's compartment the
firearm or ammunition shall be contained in a locked container
other than the glove compartment or console.