This is a huge flashpoint topic, lots of potential for harsh words and recrimminations. We had a hard-side camper on my dad's truck for 15 years, with a regular cab, and for long distance hunting trips there was no way we were putting 3 big men and one 110lb woman in the cab, let alone two 60lb setters. So somebody was going to ride in the camper. It was illegal as Hell, but it worked for several years. Then I got a dedicated dog trailer, with built-in waterers and food dishes, not to mention ventilators and a fan. When Dad got an extended cab, we thought we were all (humans and canines) in hog heaven. Four humans in the cab, two or maybe three dogs in the "Hilton" as it came to be known. Eventually, Dad bought an all-aluminum dog trailer, with 6 separate boxes, each big enough for 2 dogs in a pinch. This has hauled our canine pals, plus all of our luggage, from the Seattle area to South Dakota every Fall for ten years. When it's really cold, the insulation in the trailer and the dog's body heat keeps it quite warm. The aluminum trailer is known as the "Westin". For shorter trips the dogs ride in the camper if we take my truck, in the cab if my dad drives. Travelling in 90+ weather the camper never seems to get any hotter than the ambient temperature. If it's frigid outside, we turn on the furnace, it works fine underway. That's probably overkill, but it doesn't burn that much propane to keep them a little bit more comfortable. I guess where I'm going with this is, just about any system works if you use a certain amount of common sense. All of the cattle dogs around here ride loose on the back of flatbeds most of the time, they are just trained to stay put. By the way, I jacknifed and rolled the aluminum dog trailer on a sheet of ice in January while chukar hunting one year, the dogs weren't real happy with me but not ONE of them sustained any injury at all.