From the Everson's point of view, nothing really changed, the father Henry continued to drive along, with his wife in the passenger seat. Rick and Sam continued their squabbling, with Debra caught in the middle, all continued without missing a meat, the 'heat wave' barely noticed and forgotten about dismissively.
None of them noticed, or rather, couldn't notice, as reality changed around them. For starters, their clothes dissolved off them. This was actually in its own way a mercy given how insanely impacted the car was with the various 'shopping stops' the family had made along the way. So the loss of their luggage actually gave them some breathing room. Not that they needed to breath anymore anyway.
Their skin had become bright and shinny, a mouth-piece valve having appeared where their belly buttons had been. The father and his sons now only had a bulge of air between their legs, and nipples had vanished as well, and all openings on their bodies had sealed up except for their mouths, Linda and Debra's space between their legs and smoothed over flat. Their hair had become a solid part of their body mass.
their bodies moved with a natural rubbing and squeaking that they couldn't have noticed less, having heard them their whole lives. Seam lines formed around the sides of their bodies.
But this wasn't the end of the change, the real change began as their ears vanished and reappeared as triangles on top of their heads, their faces pushing out to muzzles, their feet became digigrated, and their hands like paws with thumbs, a set of large tails poof out of their tears, their entire bodies one piece of inflated rubber.
Effectively being living pool toys/balloons, but with more than enough weight and mass to avoid being blown away by a stray breeze, their chests were white, as were the tips of their tails and the inside of their ears and the under side of their muzzles, while their hands and feet were black. Henry 'fur' (really shinny rubber) was a bright red. Linda was similar if a slightly brighter shade. Debra was a hot neon pink, while both her brothers were a pastel blue.
The family of latex foxes just continued their drive, oblivious to what had transpired. And if they'd looked at their family photos, they'd have found a family of latex foxes as they remembered.