Larry can't tell you off the top of my head, but it was a commercial green house equipment supplier. I'll do some research and see if I can come up with a link.
The thing was the 'Bee's Knees' for starting plants as you didn't care what the weather was as, with the heavy plastic sheet over the top, you had a mini-green house that just flat worked. With the grape starts I didn't bother to build a plastic pipe frame over the top, but with 'regular' plants, that would be a good idea.
The one thing I do remember is the unit came in several different lengths, the one I had at 12' was the longest available (at the time).
Back at you later.
Larry, here's the type of thing I used. Don't know how large you need but here's some choices on Amazon.
Bigger units: http://www.phytotronics.com/Redi-HeatMats.pdf
Google plant propagation mat for more hits.