I was out in the shop and got to thinking about this thread. I rounded up a battery from my impact driver, a tester and some foil tape.
The top side does indeed conduct very well.
And so do the edges.
But not the adhesive side.
Personally I would still avoid using foil tape on heat tape if it is going to be exposed, but it looks like the adhesive will provide an insulating barrier.
Any way hope your project is coming along nicely.