I've never used Sketchup before but yesterday decided to download the free version and learn how to use it. Once I got all my Illustrator bias out of the way I found it to be intuitive and really quite good! I am sure I have a long way to go and will come back to that last comment and regret it!

Anyway, the coal hole design had started to come real in my mind, so why not use Sketchup to prove it?

Here is the standard view with the coal truck platform under the tank and the coaling track to the left. The water pipe is not in place yet (how do you bend an extruded pipe?)

This is the view along the coal truck track which is elevated by 3 feet (12mm). The door color is a distant approximation to LM® red.

And lastly, a view from above:

The tank dimension is 25 ft x 25ft in plan view.