This resource was originally created by user: kingtool on the TrueNAS Community Forums Archive. Please DM this account or comment in this thread to claim it.
A freely available 3D printed bracket and duct for a blower fan. Fits everything within a single slot. Link has info on compatible fan and installation, which is friction-fit onto the heatsink.
https://www.truenas.com/community/resources/blower-fan-bracket-for-dell-hba355e.246/download