Even after plenty of use, I still have to really put some effort into securing the lids on my fermenting buckets, I use the brewcraft 30 liter buckets, but you should hear the lid snap shut several times as you go around the edges.
I always cover the primary with a lid and airlock. If you are using a 7 or 8 gallon fermenting bucket for a 5 or 6 gallon batch of wine, it'll have plenty of space in it for oxygen a it starts to ferment, and I don't worry about those freaking gnats or fruit flies getting through the cheese cloth. Never had a problem.