I can see how that would work for you, but as i have a large fan to suck the overspray out there will be damp air being brought into the garage as soon as the fan is turned on, so dehumidifieing the air before spraying probably wouldn't help much because as soon as the fans turned on that air will be replaced by damp air from outside... You say you are going to, take plastic sides off two ends and open the doors to get rid of the overspray/fumes in the air after an hour get heater back on,, I would be careful doing that because if you let the van cool down for 1 hour and then put the heat back on, that sounds like a recipe for condensation on your fresh paint?