Firstly, temperature (kinetic energy) does not equal heat (the transfer of energy). A stepper motor generates X watts of energy ( J/s ), the heat gun generates Y watts. X is probably less than 100w (?). Y is probably in excess of 1kw.

Secondly, I look at these mounts as a metal studded rod mount with MDF spacers, the metal rods (in tension?) provide a lot of stability, the MDF (in compression?) doesn't really have any where to expand into.

Third, the shaft coupler should take up any small variation.

Feel free to correct any of this, as if an invitation was required lol.