My kids show rabbits at the local fairs. They are more sensitive to heat than even dogs and there is NO ac at the fairs. For the comfort of our rabbits we freeze soda bottles that we've put water in and place them in their cages. This allows them to either cuddle up to the ice bottle or move away from it. When driving we buy battery powered fans and place them on the rabbits. I'm sure the same tools could be used for a dog. Fans and ice. You could even freeze water in a bottle and place it in their water to keep it cool. Then set up a fan in a part of the camper to help them cool off, make sure it's battery powered.
1964 Overlander pulled by 1985 diesel Suburban 3/4 ton 4x4 w/ 4" lift & 35" tires.
Also: 2008 Sebring convertible; Camaros: 83 Z28, 78 Z28, 78 (7 yr olds); Trucks: 67 Suburban, 63 Chevy 1/2 ton (10 yr olds), 60 GMC 305 v6