Until we come up with a better solution, we made our own (like racerjoe suggested). We cut a piece of 2" foam rubber to fit the skylight. We then covered it with a piece of material we had on hand. Then we hand sewed on the side facing the sky a piece of 1/4" foil coated foam (available by the foot in any hardware store). We put it up and down using velcro. We hand sewed the velcro to the fabric wrapped foam and put the other pieces to the edges of the skylight. It has been a problem keeping the velcro stuck to the edges of the skylight. It keeps the heat and cold out and most important blackens the room for sleeping. We are keeping our eyes open for a better solution, but for now it works. Here's a picture:
Dick and Sharon