Hi Darryl. Bummer the tape didn't work out.

For whatever it's worth, I don't think you'll have any issue with the foil shining through. Before I started carpet I was quite concerned about this given all of the comments I read here on the forum. I also used Thermo Tec, but didn't black out beneath the seams. I had no issues with foil peaking through. I've been following along on your build for quite some time, and given your careful build approach, as long as you test fit each piece (no doubt you will), I think you'll find it's not an issue. At least, it hasn't been for me after 1.5 builds. Just some food for thought.