The FOPA (Firearms Owner Protection Act) of 1986 allows you to travel with a firearm in your vehicle providing you can legally possess that firearm in your home state and your destination state. You may legally pass through any state or city along the way while doing this providing the firearm is unloaded, is secured in an area of the vehicle where it is not accessible, the ammunition is separate from the firearm and secured as well. You may stop for food, fuel, and even lodging along the way but you may not stop to visit, see friends/family, or tour an area in those places which would not allow you to possess that firearm were you not traveling through.
With all of this, there are several states which have a history of ignoring this federal law and detaining or arresting people doing this then letting them work it out in court. New Jersey and Maryland are two of them, with New Jersey being the worse.
If you are stopped, do NOT consent to s search of your vehicle. If you are in any way, not comfortable with any of this, leave your firearm(s) at home. If you decide to take a firearm(s) with you, pass through the problem states as quickly as you legally can and don't stop for anything. Watch your speed, obey all traffic laws, and do not make yourself "seen". When possible, avoid the problem states.
I hope I have all of this correct. Have a safe trip.