I don't think you will be able to seal the cooler and attach an air-lock.
I wouldn't think sealing the cooler is critical. At least not during active fermentation.
I've left carboys open while they are blowing off to no ill effect. Of course I put the airlock back on when they settled down.
For the cooler, I would think it should seal well enough to keep most stuff out even after active fermentation stops. Probably not good for long term aging.