Although a brilliant idea and a relatively simple installation, mounting CO2 laser tubes (metal as well as glass) vertically is not to be recommended.
This has to do with debris, which is produced during operation, falling (under gravity) onto the inner surface of the output coupler leading to a reduction in efficiency together with localised heating and early failure.
It is for this reason that the manufacturers, such as Synrad, withdraw their warranty for vertically mounted tubes.
Tweakie.