Hi, Ron, welcome to FUD!
This problem has been around for a while and we had an earlier thread on it. Nobody suggested your patch, so you have added something new.
Here is my own solution, from the earlier thread. I found that Tegaderm was not enough, since my allergic reaction was as extreme as yours:
I just removed a G6 sensor after ten days (wow! full term) and the only skin indicator was a small red bump. I used the technique from the YouTube video described above, a 3M Nexcare waterproof Hydrocolloid pad in size 6XL (about 3x4" or 75mm x 100mm) and punched the hole with a 1/8" leather punch backed by a piece of wood. Covered the whole thing with a big patch of 4" Tegaderm to seal in the Dexcom adhesive. It was a great relief that it worked!
And here is more on how to put the patch on the sensor before putting the sensor on the skin:
I found the answer to how to apply the barrier film under a Dexcom patch: you punch a hole in the barrier film, then remove the sensor patch paper with the code number and apply the sensor patch to the back of the barrier. Then remove the paper protecting the barrier film’s sticky side and put it on and inject the wire. That way you can line up the holes exactly. A true genius posted a YouTube video of it back in 2018. Allergic To Dexcom Adhesive? Solution!!! - YouTube
I will try the patch you are recommending, but am hoping Dexcom will change their adhesive again for the G7.
Randy