Once the weather turns cold, like it is now, condensation will be a big problem. The Reflectix® bubble/foil made a big difference on the walls. You'll still need some kind of air flow. Before I had the pop-top installed I was looking at using a couple of 12 volt computer muffin fans to vent the van. A quick internet search finds this one:
12V Computer Muffin FanIt should be easy enough to mount a couple of these to a piece of plywood that would be cut to fit into the top of the drivers side window. Roll the window up to hold the plywood in place. Plug the fans directly into the power port on the dash. This fan shows a amp rating of .17A. I'd think you could power these all night from you engine battery without a problem, as long as the battery is good.
My one concern is cross ventilation. The passenger side window is the only place to let air into the van, short of leaving a door ajar. I wondered if the fans would just exhaust the air from the passenger window without drawing the moist air from the cargo section of the van. Please note that I've not tried this so I don't know if it will really work in practice. At least in theory it sounds plausible.