I was inspired by @RobBobM's innovative idea to use a temperature switch to turn on/off the BentoBox's 2-stage filter. Rob made this for BentoBox v1, and I wanted it for BentoBox v2, so I made it. :)

I used a Normally Open (NO) 35ºC from AliExpress for $0.80 USD, shipped.

This model does not have the “ridge” on the bottom because that proved too difficult to match. I used 3x3mm magnets (instead of the 4x2mm that are standard) primarily because that's what I had on hand, but it also gives a 1mm offset for more air to enter the HEPA filter. 

The holes on the top, which can be seen in this image, are for M4 heat-set threaded inserts – which aren't needed because the compression fit between the top and leads of the temperature sensor is sufficiently tight that the sensor won't move.

You will want supports (for the switch area), and they're super easy to extract.

Enjoy the fresh air!