Good afternoon, you can ck out what I'm doing on the Vintage forum under "total rebuild" I haven't done the actual extension yet, I did build my own ramp door. It would be relatively easy (if you have the equipment ect.) to build the extension, you need a heavy piano hinge and build off of that, looking at the photos on some of these trailers gave me lots of ideas. you might get away with a set of ramps that you can store under the car after loading.
Terry and Eleanor
94 Softail / 92 FXR
79 32' AMF Skamper 5th Wheel Toy Hauler
97 International 4700 Tot'r