Dear Shake and Boomer. I would like to share with you my experience regarding stable temperature environment.
Here are two graphs showing the NTP performance (Frequency error variation in ppm) of an RShake buried in a hole in the ground and a RBoom in an aluminim box with temperature changes due to sunlight and cooling at night.
RShake in my Seismic Vault
RBoom in an Aluminim box over ground.
We can await the same changes in the measured values
Pictures say more than thousand words.