Glad you asked 
Bit of MacGyver going on here. I aspire.
It took me ages, but I found the ‘fan of my dreams’ on Amazon after extensive searching (way…way down on the listings). Self powered (usb - comes w/AC adapter) , rigid screens on both sides of 140mm fans (just the correct size to fit WD USB drives depth, rubber cushion feet both top and bottom, and they can be joined together w/included metal joiners (didn’t use). Bonus - it has a 3 speed control switch. Just WoW!!
Next, Ace Hardware gutter screen. Easy cut to length needed/desired for number of drives/shelf width. Home Depot has them as well. Place on top of fans.
Last, little cushion feet didn’t lift fans to get enough air flow I desired, so added 3/4 inch rubber chair leg tips that conveniently fit over the supplied little cushion things.
I just love creating things from other things. 