This post is not as "high quality" as some other ones-- I don't have this problem myself, and never use tape underneath my Dexcom Sensors. (Or on top either, of course.)
But I've heard a lot of people saying that they, or their kids, are a lot less sensitive to 'OpSite Flexifix' than they are to Tegaderm. (One of Amy's guest comments, "Beth" on July 14, reported good luck with this one.)
Now I totally don't understand the role of Mastisol in this, so I want to gently double-check on one thing: I think that all of your reply posters are taking for granted that the Tegaderm is going UNDERNEATH the Minimed adhesive pad, with just a tiny hole for where the wire will be shot in, right?
That's how it needs to be done-- something UNDER the Minimed pad. If you're using Tegaderm only on top, and Minimed+Mastisol against your skin, that's the whole problem right there.
If the Tegaderm is underneath, the "right" way already, and you're using Mastisol to re-stick failing Tegaderm, that makes ANOTHER reason to give OpSite Flexifix a try (it might hold better, too).
Last note: A lot of people say that they two inch width isn't enough to hold really well, they're all buying the 4" and triming down to size from that roll.
And again, I'm the only poster here who DOESN'T have this problem-- give more credence to the others!