Hey Matt, welcome to the forums.
I’ve successfully used the Octo in MODEP for a quite while now, but it’s been a while since I stepped through the installs myself.
The octo installer .deb package will fail to install unless you create a ‘pi’ user, and the right directory structure for one of the install files (I don’t recall which off the top of my head, if it’s not apparent from the error message, let me know and I’ll see if I have any notes on it.).
The installer also updates the kernel, and I previously had issues with the Octo not being detected properly with some of the more recent kernels.
After the .deb install completes and you reboot, check to see if the octo is detected properly.
If it’s failing to register, then a kernel downgrade may also be necessary.
There is some info on how to do that here: MODEP no longer running following rpi-update