I looked up heat tapes used for protecting water pipes from freezing, but most of them had built-in thermostats set to 38 F.
Bare Nichrome wire is only 17-22 cents per foot, and can be had at 27, 42 or 70 Ohms per foot (36, 38 or 40 AWG).
I think you need 300 - 1,000 Ohms to get 12-50 watts from 120 V
On the other hand, "waterproof" sounds like a highly desirable feature.
And SHORT lengths of 40 AWG are used as "igniters" and "electric matches", so maybe the whole idea is dubious.
