Our HQ has the exhaust out the side and it makes no difference,fumes still come in.on our old van we had a fitted mattress that was tight against the lower tailgate and that stopped the fumes or just get a thick piece of foam(just a strip) and when you close the tailgate put the foam between the tailgate and body.if you look from the inside out with the tailgate closed there is a gap between the gate and body down the bottom and that's where the fumes come in