I did a mock up of the JD backpack based on suggestions from @WBS00001 and @ptp 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.
Other robots from Synthiam community

Jim's Armadeus Mk. 12

Wolfie's Scraps

Looks like you have done an outstanding job. Not to mention quick. Offhand I can't think of anything else. I would be more than happy to throw some dollars into this endeavor. So if it starts getting a bit expensive concerning plastic or nozzles, software, whatever, Just let me know. I very much appreciate your efforts on this.
WBS00001
same here.jd will look stunning.
Thanks Nomad and WBS00001. I'll try to print it this week and share the results. Once we know it's what we want I'll share it on Thingiverse.
@Justin,
IS possible to get a stl version of the JD backpack ?
I'm not so good visualizing 3D pictures, but a 3d viewer helps a lot!
Yes, I'll share it soon. I'm tinkering with it currently.
OK I'm done tinkering with it for now. I added some line indents to go along with the line indents on the standard JD front and I was able to move the bottom 3 slots up a little to give more room to hug cables at the bottom, otherwise it was going squish them too much.
Until it prints I'm not sure else I can do. Let me know if there are any further suggestions?
My goal is to print it and test it before the end of the week.
JDbackpackedit43.stl
The backpack is a few minutes away from being finished printed. It all goes well, I'll upload my final .stl to Thingiverse.
It's gonna need some more tweaking, but it's darn close!