Hello Island Claire,
I just came across this post of yours from last fall
. I have an identical trailer. Mine was built in 1966 and has a small die cast plate beside the door that says Buco Plastic Industries, Calgary, Canada, as well as the model and serial number. Other than that I have yet to find out any more about the company. No one online seems to have ever heard of the company.
The pictures you took are the first I have seen anywhere of another rig like mine. It's too bad the owners were never around, it would have been interesting to see if they had any more info about the company. So far it is a mystery.
I just finished pulling mine out of the garage after rebuilding it and am going to post some pictures on the forum.
Thanks for posting the pictures. It is good to know there is at least one other Buco in existence!