Conductive Greases and such with waterproof sensors?

I’m building a handful of Imp002 devices with thermistors for a wet HVAC environment. I’m building each thermistor sensor individually.

I ordered the raw thermistors, and already have on hand a bunch of stainless steel casings, but am confused about what to buy to fill each stainless steel casing before dropping the thermistors in and sealing up each sensor? I want to conduct heat to the thermistor, but not electricity.

Something with a fine nozzle tip would be best since the stainless steel casings are 2" long but have a 3/16" opening…

Might it be easier to buy pre-made stainless steel thermistor probes?

Probably. I’m trying to save money. I need about 30 of them for this stage of the project and could need up to 100 at a later point…

After reading online…I guess I will use an epoxy potting compound.

Always thought these were quite cheap, eg this is sub $5: