I made the loads for the coal cars from some chunks of styrofoam that have been aging in the garage for years. The loader in Depot Harbor was a clamshell, and would have made heaps, rather than a single big lump like a chute over a moving car. Three of the cars got three heaps, and one, for no particular reason, has two.
I painted the loads black, and then glued a layer of coal in place. That looked a little sparse and so I sacrificed a plastic bag to protect the cars while I added another layer, fixed in place with dilute matte medium.
I tried adding a washer beneath the loads for magnetic removal, but it offered anemic attraction. Real magnets hot-glued in place were much better. Some foam core feet to lift the loads off the bottoms of the car completed the assemblies.
Pembroke:87 
Very good results. I have been planning (neglecting) something similar for years. I have the supplies.
Yes, summer. Small projects are appealing.
Graham ________________________________
Actually these were done just after the meet, but I forgot to publish the post until now. But yeah, compact projects are handy when you’re travelling or entertaining.