@beneficial are you using a carbon filter on the exhaust, and do you have all of the intake vents open?
If you have all the intakes open and can’t turn the fan down enough to stop that much negative pressure, try adding some ducting, or some 90° bends in the existing ductwork.
If all else fails, some bamboo with holes drilled in the ends, held up between tent supports with zipties will do in a pinch. Not too snug so you can slide the bamboo up and down if you need to get in the tent.