I actually had a fire caused by one of these, back in 1980. There was a crawl space under the bathroom of this small cottage I lived in, in Westport, CT. Pipes used to freeze when it was below 20 degrees for any length of time. I installed some heat tape--and I cannot tell you if I did it correctly or not, but there was a fire.
In 1996 I bought a vacation home, on a crawl space...but the gas water heater was in the garage. I added heat tape to that after a couple of freezes, and that lasted over 20 years before it simply stopped working. Due to STUPID builders and electricians trying to save a couple of dollars, unfortunately the GFCI outlet that controls the garage outlet is OUTSIDE. That used to trip during heavy rains, and on more than one occasion, the GFCI outside tripped, rendering the downstream outlet in the garage unpowered. Of course one didn't always know this until it was too late. So, what I ended up doing was running an extension cord from INSIDE the home underneath the door so I could have this heat tape on an outlet NOT affected by the garage outlet.
I replaced that heat tape last year, and that new tape is working fine. The new one has a pilot light so I can see when it is on. I replaced the weather resistant outside cover with a weatherproof box, and changed the GFCI there, so it's been reliable now even in the rain.
My advice would be get the good stuff, ensure it is UL/CSA listed, and follow the install instructions. Jeff's suggestions of an audible GFCI is great. I'd consider a smoke alarm in the area where the taped pipes will be.
