Basically I put hook velcro on the inside of both set of pass through windows and made a sleeve of waterproof nylon that connects the two together. Plenty AC or heat for my two dogs in the back even going through Vegas at 115 or Montana at -20F. You will notice a little more road noise but keeps the pups comfortable, what I don't like is when one sneaks through and grabs a bag of chips out of the front when we are out of the truck for a few moments! I have a 2000 Tundra Access cab and a Hawk. I did see a double cab tundra when I was in Alaska that had a custom boot made that basically removed both sets of windows and a massive boot connected the two, it allowed someone to basically move inbetween the two spaces.