Hey BDD,
Would you happen to have any photos of your trailer with the rails?
I'm certainly intrigued about the extra storage capacity.
I've driven just about anything/everything with wheels or tracks throughout the past forty years, up to & including Michigan Trains, (upwards of 160,000 lbs. of freight, generally steel coils), and even an occasional centipede trailer (generally 6, or more axles from front to rear, and as close as they can space them), but it's been a number of years since I've been behind the wheel of a big rig. I can fabricate almost everything I need, but would appreciate any tips/info you could throw my way.
My solution for a short trailer tongue was to remove the hitch, extend it to whatever length I needed, add one more foot just for PM, then remount the hitch with new stainless steel bolts with a hardness of eight on the hargrove index, then burr the threads over with a ballpeen hammer. On some instances, I'd drill thru the nut & bolt, then pin it with a nail that I froze to shrink it's size, cut off the excess after it had expanded back to it's original size diameter.