How much Ventilation? (mr. heater buddy/condensation)

[One Awesome Inch]

When living in the van my goal would be to have a constant room temperature of 21 Celsius, about 15 Celsius when sleeping. Assuming the use of the small Mr. Heater Buddy is on the low setting, how much ventilation is required? I live in the Pacific North West where humidity is usually above 80% and I have a real concern about condensation and the inevitable mold. Thus, I want to keep the 6 x 10 living area warm yet lots of air circulation, but at the same time the less energy the fans use the better. I also intend to insulate thoroughly with 3 or 4 inches of foam board insulation.

I think I read that ideally I should have two 3 inch vents in the van... one high, one low. Is that correct?

From another thread I saw these fans which look good.

Is it better to have the intake vent/fan near the floor or near the roof?

 

[Zil]

You need a vent near the floor for the air-in, You need a vent near the roof for the vapors out.

 

[WheelEstate USA]

My friend uses 2 computer fans in his van up in Or. He has 2" foam sides and 3" ceiling.
He insulates his cockpit windows with the foil/bubble stuff.
Seems to be working well for him and his Buddy heater.