This is currently undergoing early revisions.
User Z Trick made a an inspired version of this case. Located here > https://www.printables.com/model/1388287-odroid-hc4-case-hdd-35-25
Various cosmetic improvements, better grip for the drive tray. Take a look.

I wanted a case with better airflow for the board and harddrives. The stock case relied on rediant cooling for the harddrives, and the board relied on a small 40x40mm 'case fan'.
This new inclosure encourages natural convection, and so far, has provided much lower operating temperatures than stock for the board and installed harddrives.

Assembly requires a 5V PWM 120mm fan, 4 original screws from the Odroid HC4, 8 M3 screws+nuts, and light soldering.

Light sanding or filing may be required to remove elephant's foot, or other artifacts from printing. Some parts have a low tolerance.

Moderate/Beginners may solder/join the new 5V fan to the orignal fan wires.
Experts may add a 12V 120mm fan.

Measured Temps: (House : 22C)
Stock - Idle @ 20% fan : 44C
Stock - 20% Load @ 25% fan : 48C
Stock - 100% Load @ 100% fan : 53C
CaseMod - 25% Load @ 25% fan : 33C
CaseMod - 100% Load @ 100% fan : 37C
CaseMod - 100% Load @ 50% fan : 42C
CaseMod - 100% Load @ 0% fan : 51C
**Using "Noctua NF-F12 5V PWM" (Rated at 150mA)

**Change Log:
V1.01
Top Shell : Fixed Hole Positions for Middle Plate.
Bottom Shell : Fixed Hole Position for Middle Plate.
V1.02
Bottom Shell : Added sacrificial Layer for Fan Screw Holes. (Drill bit, or something pokey required)
V2.00
Top Shell : Additional material for top-grille support. Changed internal geometry for drive caddy slides.
Caddy : Handle and thickness redesign.
V2.01
Caddy : Additional holes for 'optional' screws from SFF-8300 3.5" Drive Mounting. Indicators for 2.5" or 3.5" mounting.

Context for 'Graphs'
Squirtle was the prototype, printed in blue. There are no before and after temperatures for Squirtle.
Charmander and Bulbasaur were retrofits that have before and after temperature figures.
Charmander and Squirtle have 3.5" HDD in the rear slot, and a smaller 2.5" SSD in the front. Bulbasaur has a pair of 3.5" HDDs.

Yes