To deal with the fan anomaly of the mamba device, I wanted to be able to utilise the ability of LEDE to build a per device rootfs as here. To this end I created a Makefile to allow selecting the @gufus fan_control as a package which allows you to add the fan_control package solely to the mamba build.
As a custom feed:
echo "src-link myfeed ../myfeed" >> feeds.conf.default
mkdir myfeed;cd myfeed
git clone https://github.com/anomeome/fan_control
./scripts/feeds install -a
You should then set as loadable package ("m") menu item Extra packages/Custom feed/mamba Fan control. Then as outlined in the link above, select the per device rootfs item, and append to the mamba device the "fan_control" package.
Caveat: As my build overrides the the default crontab with a custom setup from /files directory I did not have to deal with the default fan_ctrl.sh script. You may have to comment that out in your crontab if you are currently running with the OOTB setup.