Greenhouse: Help! need vents, 0 by Texasgrower

Texasgrower wrote:
My husband accidentally threw away the vents for my greenhouse. They were with a 6x8 poly plastic, aluminum frame greenhouse. They were plastic and looked like a grapfruit from the top. They opened manually. The vents would snap on to the plastic like a tupperware lid and then we were to cut away the plastic. Does that make sense?

My problem is, what do I use as a substitute? I can't find anything like them on the web. I don't know the manufacturer because the hubby through away the paperwork. (GRRRR) I would appreciate help as moisture builds up quickly. We are going down to freezing tonight and plan on putting a propane heater in there. I have slipped little hoses through the floor of the house to help air get in. There is also a 1x1/2 in gap at the door latch. Is there something I can do tonight to vent it somehow?