Many major tourist attractions (amusement parks, etc.) will have pet boarding facilities on site. Even the smallest cities now have "doggie daycare" businesses, and if you are staying at a campground you can always ask the host or a neighbor to contact you in case of power outage, etc. There are remote monitoring systems that can work with your cell phone to alert you if temperatures get too high.
Cover the windshield with a sunscreen, open the vents and use backup, redundant systems (battery powered fans, cooling pads, ice water, etc).
