We have this Bulldog coupler on our 3-axle GN trailer:
https://www.etrailer.com/Gooseneck-Trailer-Coupler/Bulldog/BD0289500300.html. Works well and is a solid coupling. Can be a right PITA to get aligned properly, though.
Tried to get Dad to order the hydraulic landing legs since we were already getting the hydraulic ramp, but he didn't want them. I should have insisted! :B
Lyle