Boxcar security at turn of the century?

A question not limited to Narrow Guage:
At about the other turn of the century (years 1900-1910 or so) what kinda security was there for regular freight in boxcars (and also for empty ones)? Did they keep 'em locked with padlocks or anything at all?
The reason for my question...A friend is writing a mystery / adventure book for children and wants to have her facts right. She plans to have the "hero" (or maybe the villian, she is still working that part out) stowed away on a boxcar, only to be discovered when the train is stopped due to a hotbox. (All this circa 1903).
Cheers from Dallas!
-Clyde