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By the looks of it there is NOT enough room internally for 20mm thick fan. I attached a section view that shows there is a slot in some of the covers already for a ribbon cable noted with a 1 in the pic. 2 shows that with the fan mounted internally it could still be hard to route the cam ribbons cable past the fan but looks feasible if done carefully. So there is ribbon cable access but maybe not feasible with an internally mounted fan. Good Luck.