I think you are going to want steel......
The guy next to me at the marina sails a 25ft boat off it's trailer. He has a slick extension for his rig. It is a long (10 ft or so) square section steel tube, on the front it has a hitch, the same as the trailer. At the back, maybe 2ft from the end, there is a hitch ball that goes into the trailers hitch. At the very end is a U-shaped piece of steel that wraps around the trailer tongue and a detachable pin passes through it to attach and remove the extension. Looks very secure when it is all set up and gives him about 8 ft of extension.
