From 1984 until now I've been a competitive handgun shooter. I've participated in matches all over the world. I've carried a weapon into places (like Japan and Moscow) where the country is often cited as being nearly impossible to legally possess a firearm. I've been fingerprinted, photographed, had my gear inventoried, rounds counted, cases inspected, test fired, cataloged etc. Jailed once only to be released an hour later, I've even bribed a customs official or two in a couple of countries - as that's how its done.
While I wouldn't consider myself an expert in all aspects of firearm laws, I am someone who has been there and done that.
1. Traveling across state lines is covered in The Firearm Owners' Protection Act (FOPA), Public Law No. 99-308, 100 Stat. 449 (May 19, 1986), codified at 18 U.S.C. Â§ 921 which has been mentioned many times here. It pertains though to simple federal rules. States and various jurisdictions can and will inact their own.
2. Getting a CHL/Carry permit will generally never be a bad thing and has been pointed out, many states have reprocity agreements allowing carry from one state to another. However in the foreign state, you must follow their rules (This should be common sense, but sometimes it needs to be reinforced) To find out which state has reprocity with which state go here: http://www.usacarry....ocity_maps.html (though for offical information go to the state itself)
3. Open-carry states are very specific to how open carry works. Reading the law is helpful here as "sitting on the seat in the vehicle" isn't exactly open carry in some cases. A reasonably good place for consolidated information is here : http://opencarry.org/ (again check the state before walking down the street with your six-shooter strapped to your side)
4. Traveling into Canada with a handgun is permissible, if you obtain the appropriate permit. http://www.losttarge...earmcanada.html is a good source of information on this. I myself have gone through the process a couple of times, most recently this summer when traveling through Canada from MI to NY (NIagra) It took about 5 weeks for the appropriate permit after I sent the paperwork. Going through the border this time was as simple a showing the permit and getting waved through.
5. Traveling into Mexico with a handgun is also permissible, with a permit, though it is much more difficult to obtain .. You get them from the Secretariat of National Defense and last time I did this, it took about 9 months. The laws here are crazy strict though and I wouldn't recommend pushing your luck.
6. A good reference for other countries http://www.cruisersf...untry-1641.html
7. If your rig doesn't have a good hard-attached safe, consider getting one .. Store your firearm there. Consider this .. You likely won't be carrying it on your person all the time, and you need a place to store it. If someone breaks into your rig, you want to reduce the probability that your gun is stolen as its now one more gun on the street. I don't personally believe that you can hide them well enough to prevent them from being found. A safe is a better answer here. *and* at least in the US it takes a court order to force you to open one .. Giving you time to get a lawyer should you need one.