USB Failure and Repair - with note on Radio Installation

[Galway Girl]

Our EII Hull 505- 2019 had been having some weird intermittent USB action on the street side of the trailer.

When I checked for continuity across the 20A 12V Fuse (Street Side) in the rear attic it showed all OK.
I removed the 4 screws that hold in the radio, pulled it out and checked the voltage on the connectors for the USB plug leads and read 2V.
I went back, pulled the fuse and measured a resistance that was pretty high and noticed discoloration in the fuse body...

It turns out that fuse has partially blown.
I replaced the fuse and measured voltage at 13.4V and when the power and ground reinstalled the USB ports came alive.

Upon re-installation of the radio I noticed the bottom right of 4 screws was not actually going into any fiberglass.  
The hole cutout for the radio wasn't a clean rectangle and that bottom right screw is floating in air.  
I'll be trying to find some c-clips to use as a backer for that screw.

Craig - Hull 505  2019 EII