My wife and I bought a house about two years ago. Okay it's not a custom built fermentation closet it's a sauna. We rarely use it, it stays 66-68 degrees year round, it's big enough for around eight people to sit in, and it has no light or sunlight going into it. Perfect fermentation closet.
What kind of brew pot are you using that leaks? Are you sure using sealant to fix the leak is the best route?
-throw away leaky brew pot
-buy new bigger and better brew pot
-new brew pot doesn't leak