I've been fermenting in a kettle for a few years. Usually ferment 10 - 14 days, then transfer to a keg, let that sit warm for another week or two and then cold condition and serve. The intention is to get it out of the kettle not long after active fermentation subsides. Sometimes I seal up the kettle w/ plastic wrap / plastic bag and a string wrapped tight. No issues to date, try it, airlocks are for aging not fermenting IMO! I brew ales that are intended to be consumed fresh, say within 2 months and will be stored cold...if I was looking to store warm, or cellar the beer for a year I may not be as cavalier, as infection and oxidation occure much faster at higher temps...but how quickly does infection or oxidation happen in a 30 some degree keezer? I doesn't IME.
Beer is pretty resilient to infection and oxidation IME if basic care is used...ESPECIALLY during active fermentation!