I do this if a wine is in the 4-6 month range. You only need an airlock if your wine is degassing. It's technically a one way valve. I either cap or go to a solid bung. Then I don't have to worry about water levels.Why is it capped?
Sometimes I'll add the extra security of plastic wrap and an elastic. I've pushed some to 6 month K-meta additions. I figure air is only getting in if I open it, so why disturb it.