I did a mock up of the JD backpack based on suggestions from @WBS00001
from my C3PO JD head post.
It has a male clip on the bottom to slide into the 3rd middle female slot inbetween JD's legs to anchor the backpack cover. It also has two posts that slide into the top two screw holes of JD to help steady the cover.
There is a dual female slot on the back where you can mount 2 things like sensor modules or light weight items.
I opted not to add a male clip at the top of JD as the other anchor point. I don't think it's needed for a cover, but I may make an alternative version and incorporate that idea. I feel like it would only be needed if you wanted to do something extreme like mount a 3rd foot or 2nd head.
There are open slots on the top, bottom and sides for wires and the switch side has a big enough opening "most" fingers should be able to still access the switch.
I have not print tested it yet, I wanted to share the rough draft first for feedback.
The backpack as it would appear on JD:
The backpack by itself.
I welcome suggestions and input. I think this is a community project.