I ran a number of 5830s out of the garage over the summer and asides from a thick layer of pollen and a few mangled bugs everything was fine. If I were to do it again though I'd duct the rigs with cardboard and use some box fans w/ chopped up furnace/AC air filters to filter the air a bit. Will have to find a similar solution for this upcoming summer as the rigs migrate outside the house again.
No offense, but there are good reasons to not do 24/7 unattended electrical operations with flammable materials.
While I've been known (in my much younger past) to run a machine in a static wrap bag (to decrease cat hairs) in a cardboard tray, I would not attempt to run my mining gear this way. I thought it was dangerous to make that PC work that way - 24/7 equipment that runs at full tilt boogie can experience unexpected events. I have responded to alarms on gear that turned out later to have melted, or caught fire in the switchroom/datacenter.