I played around with the BentoBox v2 and the LunchBox and decided I wanted to do my own version. I reversed the airflow direction to avoid blowing on the 3d prints, plus it seemed more space efficient.

Printed parts

This is how the parts fit together from bottom to top:

1. Base- holds the HEPA filter
2. 3× Carbon tray - The Bento Box uses a three baffle system, so you can print three of these and stack them for the same effect.
3. Carbon lid - holds in the carbon from the top tray
4. Fan tray - holds 3 40x28 fans with a wire guide, make the fans blow up
5. Fan lid - fits on top

Magnets are used to hold sections together and pegs used between sections. Basically you don't want to spill the carbon material everywhere, right?

Shopping List

1. 20 3x2mm magnets
2. HEPA filter
3. Arctic 4028 PWM Fans are what I used
4. Noctua PWM fan controller to adjust speed if you want to moderate it
5. 3 fan to 1 PWM adapter
6. AC to fan power supply
7. Carbon media

I had a lot of these things lying around, so there are probably cheaper options out there.

Wiring

You can use the whole on the other side of the printer like everyone else does, just remove the pins from the connector and feed them in individually. Or just pull out the drill.