Cooling the campershell for dogs
 

Yeah, I do it. I open the rear cab window and camper shell window. I point the rear seat ait vents right at the open rear window. It gets some cool air back to the dogs.

You might be able to rig a fan in the rear window to blow air into the bed. But it would have to be very cold in the cab to be able to cool the bed area since the shells aren't insulated, and the sun will heat up the shell a lot turning it into an oven.

I would probably try to consider other options if it were me.

Turn the fan way up and close the front vents. While not perfect it does get a good amount of cool air to the shell. I point the rear seat vents right at the rear window. I have done this traveling across the country several times and it works fairly well.

They make these little air hoses that you can pipe in the A/C to an area like for babies and children in the back of your car. you could try using that and put it through the back window

But have you checked what the actual temperature is inside the shell both while moving and while stopped? In strong sun etc? Remember you have a live animal in there, and just climb in, close it all up and hang out in there for a while and see if it's actually comfortable or not. The cool air might not make up for the radiating heat from the shell. You have to also be aware of any exhaust fumes getting in there, especially if the shell has an open slider/window on the exhaust side.