Hiding a 12ga inside a car bodywork is easy peasy lemon squeezy and slugs from that reliably put down grizzly bears, which are I believe the toughest land predator currently in existence.
Trying to cross international borders legally with a firearm for self-defense is really difficult if not impossible. If you talk to Overlanders or international ocean cruisers, almost none of them carry weapons. Trying to sneak or bribe your way across a border with a weapon is a pretty serious crime.
[1] http://www.thehighroad.org/archive/index.php/t-65646.html