This is such a difficult decision when going into a bank or grocery store you need to have a thermometer adjacent to where the dog is being kept, if it's in a crate .. I happen to have 2 - 12 volt osculating fans with deep cycle car batteries attached blowing inside the camper shell - cab window is open in front the shell windows are open and back the shell would be open in case the dog needed to be taken out quickly -- but this is such a difficult decision you don't want to leave your dog home -- you want to take the dog with you -- you need to make a quick 6 min. stop it's just difficult all the way around if you're by yourself . In as little as five or six minutes the temperature can rise 25° if you're not in the shade . A magnetic sign wouldn't be a bad idea either ..