Hydro farm heat mat thermostat

[River]

After I planted my various tomatoes I read the instructions on how to use the thermostat.
I had an issue with the probe staying put plus the plastic top. You cannot keep The top tight.
So trying to keep the probe in place is tough. I see a little rubber suction cup

Please tell me what the instructions left out

[GEOSAN]

forget the suction cup...use a little piece of ductape to secure the probe wire to the side of the container. That's what I do. And the plastic top...on what ? The seed tray ? if yes, another small piece of ductape works for me.