Being from British Columbia, we have a small tourist industry based on hunting our big game, many come for this from Europe. They come with some amazing rifles, of course this is all legal. When we go south there is usually an interesting tale to relate about the last crossing, around the campfire.
Traveling to Mexico for several years we never had to leave our motor home for their checks that sometimes took place; this is different nowadays, both at Canadian, and the US sides of borders. If you are sent to "agricultural" or other line ups, you will give up your keys and wait after a few questions, then that person will tell you to take a seat and will check out your vehicle(s). They will leave it unlocked more than likely and you will need to check over your towed vehicle, making sure that gears are still set right, and you're on your way, maybe giving up your rice kept in another small container other than the original where it's origin could have been determined.
An exception was one stop when we were driving out of Mexico, entering Texas. It was our first time in Texas, and the officer checked the coach with my wife present, and the dog sniffed both there, the outside bays, and the car. They were very pleasant and gave us many tips even about where to find the best shopping, only taking a small container of yesterday's cooked pork. We are not full-time RV'ers, do not carry firearms, have never smoked marijauna. On that last question, answering in the affirmative will immediately yield a lifetime ban from entering USA.