Any issue using MDF as the little miner box I built? Temps are not over 85, wood doesn't feel hot, or anything like that just wondered if I should have used a metal shelf just in case something were to go crazy. before this, I was using the cooling mod when I only had one S9
I guess no matter what a fire would be fire just curious a few expert thoughts.

Honestly, I think you would be fine, as long as you have a source of cooling of the S9 itself. Include 2-3 inches of space between the miner and the upper wood, side wood panels, and use fire-resistant lumber if possible (but not required); it would need a slightly massive, consistent electrical fire to start that wood burning with a buffer like that. And those types of electrical fires are somewhat rare, especially if adequate cooling and space are there when constructing a cubicle for miners. Of course, anything is possible, just not probable.