I actually ended up getting:
https://www.logic-case.com/products/rackmount-chassis/4u/4u-standard-chassis-15-x-35-hdd-sc-415h/
The front fans pull air through the front and blow over the drives, and then another row of fans behind the drives pull the air from over the drives and push over the hardware.
Its currently in a really warm room, and drives are around 33c doing a full on parity check, so constant use for a good few hours.
But the fans are pretty loud for the room its in, currently moving so in the new place I'll put it in the garage where it can hum away as much as it wants.