Here are some easy ways to load up your gondolas.
1. Dirty up the empties - Empty model gons have two problems: they are too light, and too clean. We can add some weight by placing a flat steel weight salvaged from a boxcar right on the bottom. The weight from a 40' box car fits nicely in a 40' gon, as seen below. Next, we will dirty it up so it is not so obvious what we have done. Gons always have some debris in the bottom. Gather some workbench and floor sweepings, sift them through a colander or screen to eliminate the big chunks. Paint the bottom of the gon (or the steel weight, in this case) with thinned white glue and sprinkle a bit of detritus around. A little goes a long way!