The dog injury story I just posted reminded me that I never circled back on this topic.
I ended up finding a great deal on a used Leer 100XQ (facebook marketplace) that fit my truck and was in very good condition. I was worried about air circulation for the dogs with that model, but I took them up to the cabin at the beginning of this insane hot spell and the air moved through there just fine. I found that closing the rear truck cab window, opening the front window of the topper (closest to the cab) and venting the side windows as far as they go provided the most air circulation. We stopped a couple times for restroom breaks and snacks which gave me an opportunity to give the pups some water and I'm sure that helped quite a bit as well.
