The T-probe needs to be inside the enclosure, directly on top of the hot spot.

Do not put it on top of the substrate, since most BP's will move the substrate and if your were to do that it would risk being burned (since the temperature under the substrate would be too high if you're measuring the top of the substrate).

I'm not 100% about boaphile, but with our enclosures electrical tape works best. There are risks with using tape, so I'd check with boaphile to see what they have tested first. Assuming they have been testing their products that is.... (if so, please post it on here so everyone else will know what they recommend).

No matter what - always keep an eye on the tape. If the corners are coming loose - replace it!