Something I found that helped for fishing the wire through the hatch grommet. I used a wire tie (Just like the ones you used to attached the wire to the grommet.) I had a long one and ran it through bare with no problem. Then I taped (Using electrical tape) a long portion of the camera wire to the wire tie (Again, a long wire tie is better for this reason) and with some massaging of the grommet, was able to make it through easily.
Now this was on a Blackvue. Your mileage may vary, but give this technique a try and see if it helps.