Here's what I did/didn't do... We went full time in August while we build a new house that won't be done until April. I had this very same concern with my two dogs and summertime temps @ 100+. I explored several options but ultimately went low tech... ie nothing.
Fortunately my wife and I work just a few miles away and since both dogs are kenneled, the old dog because he tears up the screens and the pup because she tears up everything, one/both of us go by each day during lunch to check on the dogs and let them out to take care of business.
I eased my mind about doing nothing, with an experiment. On a Saturday we left the trailer at noon with the AC off in the heat of the summer and returned @ 5PM to an inside temperature in the high 80's. Uncomfortable but not locked inside a car in the summertime fatal.
Some of the other things we've done with the dogs to adjust to full timing... occasional doggy day care at my daughters with her dogs and a big back yard, we normally take the dogs on weekend trips (yes I take my house tailgating) but we found a nice kennel that the dogs love and stayed at for a week at Thanksgiving, Christmas & New Years, and I try to walk the pup every day, the old guy doesn't care.