Ted I saw some plans somewhere for a germinating box using a string of christmas tree lights(Not LED) placed in sand which provided an even heat source.. Sand was 1-2 inches deep and I believe aluminum foil was placed on the bottom to reflect heat up. The box was built to dimensions to accomodate the transparent cover which I think was just the clear plastic type used in the type ofgerminating kits sold by walmart and other stores. Of course, you can make the sides of the box tall enough so that could just use clear plastic.
Or, you could just buy a heating mat and miss all of the fun and feeling of personal accomplishment as well as possible frustration.
As I have no personal experience regarding this design(caveat emptor) I can not say how well it works but, I plan to try this idea for the coming germinating season.
Jon
