I don't know about the piss test, but I do know that guns and ammo are VERY expensive down there. I was stationed there in the early 90's, and married one of the best women that panama had to offer(no, my wife does not read this website). It probably helped that her father was a gunsmith, the first time i met him i fixed a browning shotgun for him, instant friends. They do tend to not like "military" style guns, but there are alot of fudd guns down there, most common is 22lr and 12/20/16 ga shotguns. There isn't any fixed hunting season that I know of, and the deer are freaking tiny. I used to go down there with the wife and kids for vacation and take as much 22lr with me that i could for the FIL, he went crazy of the wally world bulk packs. Panama is a wonderful country with many great sites to see, if you get a chance, go, get out of the city into the country, there are alot of poor people, but that is anywhere you go in the 3rd world places, but most are friendly enough. Plus if you get to know some of the locals you can get some really good deals, I got an original spanish sword (kind of jacked up a little, but still sharp) for 10 bucks, it resides on my wall at home. As long as you are not buying guns or ammo, the US dollar goes a long way down there.
Chris