Remember, the key issue with the oil door and hinge is how much it will flex.
The inside of the cowl is pressurized. Check it in the shop by placing the cowl upside down on sawhorses and applying about 5-1/2 lbs of lead or similar in the center of the door. 5.5 lbs is 4.2" H2O applied to a 6x6" door, and would be about right for a standard RV cowl exit area at 200 knots VNE. A more closed cowl exit would increase door pressure to some higher level.
A door which bows outward is a significant drag producer. Worse, you gotta look at it while you fly.