My advice also is get a swampcooler (or build one) , you can build one with 2 fans and 2 pumps, so it will be redundant if one fan or pump fails. But I been using swampcoolers for the past 4 years and a fan or pump failure is extremely rare and I run them all day long on the weekends. Just make sure the dog can't reach the power cord to pull it out.
The one I use right now uses a max of 3 amps at full power with 2 fan running. You can run that all day just on battery power alone, with solar you can run multiple swampcoolers at the same time.
The bigger ones I built with car radiator fans (use about 6 amps) put out the same air as a fantastic fan. Those fans arent as robust as the smaller 120mm fans, but using everyday they will still last you about 1 year.
With swampcoolers, the misinformation that they don't work is that they arent setup correctly. They need to have outside air to work. In other words the air intake needs to be right next to an open window, or like mine be ducted to the outside. Parked in the hot sun, regardless of outside temp or humidity, the swampcooler will cool you down. It won't cool the whole van but your dog will be smart enough to lay down next to the swampcooler hopefully. And depending on the temperature, the swampcooler might use 2 to 4 liters of water all day long, the small swampcooler I use holds 2 gallons of water and can run all day without refilling.
The holy grail for real AC use is "lithium batteries" and then figure a way to fully charge them at night.
Picture of side vents I use for my swampcooler. Without ouside air swampcooler will not work, it will just recirculate warm humid air.
small swampcooler