My vent kept leaking. I called the manufacturer, and they sent me a new one free of charge.
I agree, they really heat up. I'm ordering an automatic vent opener. It's the vent "hinge", but filled with oil. When it heats up, it extends out, opening the vent automatically. Last year I nearly baked an Owari Satsuma to death. I don't grow any thing in there during the warmer months, but still keep it opened up, and use shade cloth to help keep the temps down. My shade cloth is just a couple of cheap tarps I found at the dollar store, but works perfectly.
In the winter I use a space heater with a thermostat to keep it warm. Works well enough, but wish I had bought the double walled greenhouse, instead of the single. Works great for starting seeds, and keeping my potted plants from freezing in the winter.