Success! I decided to try the heat gun method and it worked like a charm. As John and Mike advised I took it very slowly and the tape pealed right off. I found it worked best if I pulled the tape with a gloved hand at about a 30 degree angle to the seam and held the heat gun at the same angle so it warmed the area in front. A few times the tape separated but I was able to scrape it off with the putty knife. After a bit of light sanding it looks great. Unfortunately, I was alone in the shop and don't have any photos to post. I do have a couple very small spots--hardly noticeable- that I 'll try to eliminate by the fine sanding method. Next step is to heat the shop up to 80 degrees or so and redo the seam using 6 oz strips cut at 45 degrees to the bias. I may well leave the other seam alone and will make that decision later depending how the sides compare visually. I doubt there would be a structural problem as I used the same tape on both inside seams which I understand are the most important.

Thanks again for the help.

Ian