the laws are all over the place...in PA you can transport a gun (any gun) in a car BUT only to/from your home and an FFL, shooting range or hunting (with a hunting license) and you many not stop- at all - gas, piss, food - sorry, that's a stop and it's a violation.
Penalty is you may never own guns again. Stiff one, huh?
BUT you can get a concealed carry permit just for asking - we are a must-issue state, no reason needed. Then you can carry concealed, open, in your car, in your lap - whatever.
Most states are now reciprocal on that...but not all.
Some states list your CC permit with your drivers license or license plate so a cop knows you have, or MAY have a gun with you. PA doesn't do that, florida does. It was big news 2 years ago when a FLA resident was pulled over on 95 in MD (a very anti gun state) and his car was strip searched (as in taken apart) looking for a gun. Why? MD never said why they did it.
Many I know used to get a 'utah non resident permit', a CC permit that was accepted by many or most states - be that for real self defense, paranoia or political reasons, can't say.
I do competitive shooting and go to ohio often - never paid attention to their laws..no doubt broke many. Can't put my garand in a trunk in my car when I don't have a trunk...LOL. One could say that anywhere in my outback I could reach a gun...
A group of friends went to arizona for a cowboy action shoot - 5 of them, 4 flew one drove the gun and ammo...how would YOU explain to the cop why you have 25 or 30 guns and 2,000 rounds of ammo in your car? LOL
Never heard of anyone but the FLA guy (whose gun was in FLA) that had issues.
My concerns are having an accident and you're in the hospital and your vehicle (and guns) are god knows where - here they do not secure vehicles towed from accidents.
Or you break down and get towed, the vehicle is a strange town/shop/area and your gun(s) are in it..or on you which may be illegal.
There are work arounds for all of this of course.