the P180 will warm your drives up like you won't believe, even without being blocked. part of it is the silicone grommets for the mounting. yes, they insulate vibration, but they also insulate heat. the screw->case heat transfer isn't huge on an absolute scale but a couple watts is huge for a hard drive. and unfortunately the bottom chamber has possibly the worst fan position ever devised. some people have shoved a slim scythe slipstream in front of the drives.
what's your fan set up for the P180, OP? without a fan in the top, usually people on SPCR and the like have been blocking the top blow hole as it creates a shortcut for air through the top to the exhaust (and a direct noise path).