It definately looks flamable! I suspect it is a home made by the railroad for hauling maintanance of way supplies to the job site. I don't know if a railroad would need chemicals or paint at a job site on the right of way or not, but that is all I can think of that would be flamable and carried in a small shack on a flat car like that.
how about gas for a torch or portable welder?
where did you find that car