I find playing the elevation to stay cool game in the summer to be rather tricky, 75+ and sunny is way to hot for me in a van, especially now that my dog is older and has a heart condition. Sure you can go sit on top of a mountain pass but then you have to head down to the valley for supplies and what not and it can be crazy hot in those valleys. I find hugging the norcal and PNW coast to be the only reliable way to stay cool during the summer. Also when I say hug the coast I mean that literally, I have had days where it will be in the 60's on the coast and then jump up to the 80's just a few miles inland.