In the deep south in summer, mine typically tops out at 105 to 107 -- but that's with vent running, windows open, etc.
It would go higher than that if I allowed it, by keeping the van un-shaded and un-ventilated. I've measured exterior skin temps as high as 146.
Heat is serious business in southeast Texas. I've done a number of improvements to combat it.
(1) Earlier this year, I added a reflective roof coating (blog post
). It's not a magic bullet, but it does help. It's a bright white latex product called Bus Kote:
(2) I also sewed a side shroud with a reflective outer cover (blog post
). It is held on when needed with neodymium dot magnets and looks like this (below). It was an inexpensive metallic fabric that I bought on clearance and you can see the imperfections in it (thread tension variability). The corresponding exterior windshield cover being a commercial product that I got probably from Sprinter Parts Depot.
(3) I also currently use Reflectix inner window coverings, except in the cab I use the Heat Shield commercially-fitted windshield and side window coverings. A few fellow B van owners in greater Houston have installed 3M Crystalline tint in the cab, but we haven't taken that plunge yet because that stuff is pricey - about $1,600 to do the cab windows alone (but reportedly it does work). Goes to show you just how desperate we are for heat control in this part of the country.
With respect to the interior window surfaces in the body of the van, I'm in the process of upgrading from Reflectix to DIY window covers that have Insul-Bright cores. That's a thermal fabric typically used in products like oven mitts and pot holders. The slider cover looks like this, held on with Velcro dots (it has a metallic overlay for style - the Insul-Bright is actually a white product that looks a bit like quilting stock):