Thanks for the inputs! I'll be building my own boiler, so I can build it with any kind of floor or slope I want...
Makes sense for the shear pin breakage right after loading. I have a propane furnace in the house for backup.

And the shop takes a LONG time to get below freezing....
As for insulation quality, in a hard winter, I'll easily suck down 20 full cord of wood (in a hi-efficiency gasification stove)... On -20 nights, I'm stoking the wood boiler 3-6 times a day.... So yah, this will definitely be an improvement.

I'm thinking about building my coal bin with a sloped floor leading down to an elevator "drag" to pull the coal out of the bin.... Take it right to the boiler.... Just open the hopper lid and feed it in!