Hi foks. I'm running a new line to two USB ports.  Tying both positives together with a wago and into an unused fuse spot on the back of the fuse panel.  Tied both negatives together with a wago, but looking for advice on where to tie it in.  There's not a common negative bar on my panel, but there's a ground bar on it with a single copper wire plugged in to one of about a dozen spots (the others are empty).  Should I tie into one of those spots on the ground bar on the back of the panel?  Tie into one of the other white (neutral) wires near the panel?  Something else?

If this question is answered somewhere, please let me know. I've searched the forum for a while and haven't found the answer, so posting here in the hopes that someone can answer or point me to where it's already answered. 

Many thanks.