My heated bed has NO control software. it just used nichrome wire between two steel sheets (insulated with kapton tape). Just use about 6 ohms of wire and assemble. Connect directly across 12volt supply. Measure the heat the bed reaches. Reduce the wire resistance if you want to increase the heat. I ended up using a couple of wire lengths in parallel and around 5 ohms. bed runs at a steady 110 degrees.

http://www.keegan.org/jeff/homemovies/miscimages/misc-2010/tape.jpg

There is no cover.. You just apply that to the acrylic bed (well, I had an acrylic bed on the makerbot I was using), tightly (no bubbles), and ABS will stick down pretty well (until you get to large pieces, at which point you either need to switch to PLA or get a heated bed).

then we moved to an acrylic bed, and prints would adhere sometimes, but sometimes also not adhere at all and curl (or break off entirely).

then we moved to a heated acrylic bed (~60°C). this worked *too* well, and the prints were near impossible to remove — particularly failed prints, that were only one or two layers. sometimes if your print was tall enough, you could just ‘snap’ it off and hope it didn’t break.

then we covered the acrylic bed in kapton, and heated it up to 120°C. this worked pretty well, but warped the acrylic table.

then, finally, we have moved to a large aluminum table covered in kapton at ~110°C. so far this is working beautifully, and the prints come off very easily.