I recently bought a new cover, and had it professionally installed. I got the dimensions from the manufacturer, so we should be good there. I noticed some icicles hanging down in spots, and called the guy that installed it. He said it is normal for a little steam to escape in the folders (I have a trifold), and it is supposed to so it doesn't deteriorate the cover. I wanted to get a second opinion on this as I thought these things were supposed to be air tight to keep the heat in.