Just a thought, instead of concentrating on the trailer, do you remember anything about the cab?
Brand, model, color, any printing on the door? Should be easier to find the cab and trucking company, check their schedules, and log books..If that doesn't work, you know he's an independant, but he had to be pulling that trailer for someone else..Best of luck, and hold on to the old black truck..No matter what, it's fixable when you have friends like us..Steve
