I "potted" the sensor into the case this morning. It was difficult to get it to flow into all of the voids, so I gave up on trying to do that. There is enough there to hold the sensor in place, to seal the hole for the electric cable, and to greatly reduce the air volume, reducing "oil canning" due to temperature and barometric pressure changes. Now, a couple of days drying and I can cement the lid on.
The silicone added $4 to the total cost, now at about $28.