Just to clarify:
I do not recommend or would do the preparation of the housing itself in any other environment then a quiet and dry place where you can put the required attention on maintaining O-Rings etc.
The only thing I have "outsourced" was the depresurization of the housing - so when the equipment has reached ambient temperature.
As the housing is closed and setup no outside humid air can get inside - so the risk of condensation is minimal. To be sure I usually place a pack of silica-gel below the camera.
- Stuart Keasley likes this