In our old weekender cabin there is a fairly large bore plastic pipe
that runs from the well (external, underground) to surface under the
basement floor. I haven't opened the insulation to check it, but I
expect it at least 2", possibly 3". It is exposed under the floor for
about 20' until it comes up into our pressure tank.

The exposed pipe appears to be well insulated with foam, yet since the
place is not permanently occupied or heated, really cold weather
(single digits or lower) will freeze it. While I drain the water
system when leaving, this part of the pipe is the low point, so it
never drains completely. So far no damage has been done, but it takes
~24 hours with an oscillating heater under the floor to melt the
blockage and get things flowing again.

I am planning to add some heat tape to solve the problem. What I had
hoped to do was cut a narrow strip (1" maybe?) out of the foam
insulation along the bottom of the pipe, and tape the heat tape/strip
to the exposed plastic pipe, probably with a metallic adhesive tape.
I would use a thermostatic plug, or a temp sensing tape product so it
works only in cold temps.

Wondering a few things:
1 - Is the single strip of heat tape sufficient for keeping the pipe
thawed? I figured with heat rising and all that, doing spiral wraps
would be wasteful (and require me to remove all the insulation).
2 - Can you combine heat tape and insulation?
3 - I have seen "medium" and "high" temperature heat tapes. Is there
a "low" temperature one as well? I just need to keep the pipe at 35F
or so.
4 - Anybody got a recommendation for a product that will work on
plastic pipes and be effective for this application?

Thanks!