You can travel with your gun in your car across state lines as long as the gun is legal and the gun is registered in your name and you have your permits for the gun to carry it.
The gun can be carried concealed or in plain view although when traveling through unknown states it's best to leave the gun concealed and out of sight in case you get pulled over by a cop with an attitude.
If the cop has no reason to search your car and you have not given then permission then they cannot find the gun or do anything about it.
I keep my gun under my seat and out of sight and carry it across state lines when traveling and it's never been an issue.
I go camping and mostly keep the gun with me in case I have to shoot a bear, snake etc but if I had to shoot someone to save myself then I would but thankfully that has never happened yet.
Also if you're in Kansas the state of Kansas recognizes all other states' concealed carry permits and you can travel with the gun in your car loaded or unloaded, concealed or in plain view while driving through Kansas.