Bottom Heat For Cuttings! HELP! :)

Ok, so propagation of seeds and cuttings isn't that hard and has a pretty good success rate (for me at least lol) ... how ever im currently building a new grow room and want to install a small seperate room type thing specially for propagation ... i no how im guna do it all, i hav one problem, bottom heat!!! ... I've never used it b4 and was just wondering if any1 could recommend something that they found to be good ... i been looking at those heat pad things at my local grow shop and think they mite b good or the wire things (they heat to 10 degrees C above room temp) ... how ever i dnt yet no if u can just put the wire on the ground or wat, will it melt the plastic or anything if its left on 24/7 ... any ideas or advice would b appreciated so i can increase my success rate to bout 99.5% lol, more plants yuss! ... o and has any1 seen that thing bout THC labrotories? did they say they were propagating 500 - 1000 plants a day or a week? coz that shits crazy lol