I have a 20 gpu 1070/1070ti setup going in my garage/workshop.  I just built a box with a 2x4 frame and Hardiebacker ceramic sheet for walls just in case of a meltdown.  I doubt the thing will light up but you never know.  Its a little piece of mind.   I put two AC Infinity Cloudline T6 fans pushing the air out the top and out of the house.  The main reason for the mining enclosure was the shop would just get too hot even in the winter.  And I do pull cold air from the outside and I am in a fairly humid area on the west coast of the United States.  With how much heat those gpu's put out I am not super worried about the wet air.  From the posts above it does not seem like it should be an issue.

https://photos.app.goo.gl/WZ3aWze7xU5f6w859