I have a couple of options for you but unless your flatbed truck is using a B&W Turnover ball system the only way to connect your trailer to your gooseneck hitch is to use the Convert-A-Ball Cushioned 5th-Wheel-to-Gooseneck Adapter item # CAB-C5G.
The Convert-A-Ball has a 20,000 lbs capacity and attaches directly to your 5th wheel trailer's kingpin. I have linked an installation video below.
Another option would be to change the pin box on your CrossRoads Sunset Trail Reserve to a gooseneck... view full answer...