I don’t trust the lightbulb idea because they burn out without warning.
How about two different brands of heat tape at the same time, checking each one every season, or multiple LED bulbs to equal the heat of an incandescent?
If the distance isn’t too great you can put a sensor from your thermometer in the house into the mix, to be able to know everything is working.
Here are some chicken coop heaters.
https://www.amazon.com/chicken-coop-heater/s?k=chicken+coop+heater
Two light bulbs, with one in a light sensor socket. If the bulb int the standard socket burns out, the other in the light sensor socket switches on.
If you're checking on it every week or so and find the bulb out, move the working bulb in the light sensor socket to the standard socket and put the new bulb into the light sensor socket.
If not sockets, you can buy a light sensor plug. Some, like the ones for Christmas decorations, have a timer and remote controller:
https://www.amazon.com/dp/B0711DT17X?pd_rd_i=B0711DT17X&pf_rd_p=b000e0a0-9e93-480f-bf78-a83c8136dfcb&pf_rd_r=GX96WE2B5MQ9PRF5F57V&pd_rd_wg=YVqmV&pd_rd_w=E1mZb&pd_rd_r=595ff8e6-e82d-46f6-a0fb-daf54a991f25
In one coop, I have a heater I built myself, using the steel housing from a gutted 4’ fluorescent light as a reflector, to which is mounted a small industrial quartz heater “block” (element). (The “block” is about .8” tall x 2.3” wide x 12” long with nice 1/4” threaded studs in the back.) The lead out wires are ceramic “beads” insulated. The element is rated at 230 or 240 volts usage: Run at 120v it barely glows, but still puts out a little over 300 watts, IIRC. I can switch in a series 15A diode (way overkill) to drop it to around 125 watts (measured current x rms voltage.) Even at 300+ watts it should last, well, a lot longer than I will! The weak point is probably the thermostat mounted on the side of the coop, but it should last a good while (rated for 1500 watts, is switching 300+ watts.) If I want to improve THAT, the thermostat can control a mercury wetted relay.
I “could” make up a variant of this for the wellhouse, as I have several elements left, and plenty of old / dead ballast fluorescent fixtures to cannibalize.