jonco223's design for a J1772 adapter for the trunk of a model 3. All credit goes to jonco223 on thingiverse.
From jonco223:
Utilize one of the plastic push pin clips in the trunk to mount this holder for the charging adapter.
I printed in ABS at 20% infill, no supports necessary.
How to install: https://youtu.be/SD9FAFNJass
Newer Model 3s may not have the push pin, but you can still install in that location, details here: https://youtu.be/WfFdlGZh1fw
The author remixed this model.