Heat tape generally has a thermostat built into it, near the plug, to keep it from over-heating. Otherwise, it would be on all the time. I stretch the heat tape along the water line and hold it in place with electrical tape. Then, you take a roll of insulation, about 3" wide that already has the foil on the outside, available from your local building supply store, and wrap the whole thing in this. Overlap by 1" with each wrap. I use ty-wraps to hold the insulation in place. Our electrical heat tape is left plugged in all winter long. Even with no water run for 12 hours or so, when you turn on the cold water it is just warm for a few seconds showing the thermostat is working. The foil just reflects the heat back in, like an emergency blanket does for a person wrapped in one.
DRINK COFFEE--do stupid things faster and with more energy ! Rockwood 5th wheel, Signature Untralite, 8244S
Tow Vehicle: Ram 3500 6.4 litre Hemi.