Fortbyte 13 is located East of Paradise Palms. It is in front of the mobile toilet.
You can find the exact location of Fortbyte #13 in the map below. We suggest to fly to this location, collect the Fortbyte and go to Paradise Palms to gear up.
Once you are in this location look for the mobile toilet, the Fortbyte is at this location.
This video shows you the exact location for Fortbyte 13.