It's highly unlikely the chassis manf's (Ford, Chev, etc) frame rails extend back to the hitch/rear bumper. Take a look. Extensions usually start/fasten to the OEM rails maybe 3ft/1m in back of the rear axle. When you spot where the area where the extensions attach, thinking you'll understand my concern. Not familiar with Winnie specifically, but I've never been real happy with this "feature" on competitive brands.
Another thought after seeing the pics, betting this trailer is going to be difficult or impossible to see when pulled behind the MH. Might be easy to make a good case for installing a rear view camera.
Nice to see you're taking a cautious approach. Best of luck! -Al
1997 37' HR Endeavor, 275hp Cat, Freightliner
03 CR-V Blue Ox, Ready Brake