That's what I'm. Doing next fall investing in thst set up . As my Temps hold steady around 78 ) lately in flowering. But humidity jumps all the time but dies usually hang around 40-55.Ok. Now I get it. Your tent when sealed is a problem. Your plants need to breathe. I think if you went 12 hours like you are doing you will kill them. When you close the window blind is the room dark? Do people walk in and out? Mine isn't black but it is dark enough to cause the inside of the grow tent to be black. It's a spare room, so traffic isn't an issue. From everything I've read and my own example I don't need a fan to pump air into the tent. The vents at the bottom are good enough and they are always open. I think you should get an extractor and a bit of ducting. They aren't very expensive and they fit easily in the grow tent (if like mine it has slots and hoods for it). You can add a carbon filter later if you want to deal with the smell.