Update.
For the record: DO NOT, DO NOT, DO NOT, DO NOT use rubber well nuts to attach the cargo light. It doesn't work, it's a disaster.. it spins in place and/or the rubber rips up and it comes out.
I bought some Jack Nuts at the hardware store, I'm going to try that. I research about it a little before trying. If anybody has anything to say before I proceed, please speak now. 48 hours.
Thank you.