Soil Heating Cables

I was checking out the local hydroponics stores in my area today, trying in
vain to find a trace element mix w/o nitrogen or phosphate. No luck. Anyway,
in one store I ran across "soil heating cables", designed for use in
propogation trays, I guess. The wires were plastic coated and looked to me
exactly like the Dupla ones. There was no control dial attached to it, the
package said it had a built-in thermostat that turns in on when the temp
drops below 74 degrees. The guy at the store said it was waterproof. The 48'
length sells for $24.99. They have various lengths ranging from 6'-48'. I
guess unless your tank was in a cool area, the cables wouldn't turn on, but
maybe with some fiddling by the electrically inclined, you could get around
the thermostat or something. Anyone tried these?

Kent Elliston
Sacramento, CA