Early last century, the ET&WNC built a fleet of wooden hoppers, similar to this one.
Many years ago, I built a similar model, using scale lumber from Kappler.
The problem with using the scale lumber is that it’s not the right size. :o For instance, I used 2"x9" lumber for the sides. This gives you a side height of 45", but the prototype was 4 feet. I know, not a lot of difference, but enough to throw things off. So, this time I decided I’d build a fleet of four hoppers and they would be closer to scale. That means each board is a scale 9.6" wide. Not a LOT of difference, but I will have the right height. I will also be able to cut the vertical posts to exactly fit the Ozark castings; previously I had used 3"x3" and they are a bit too small. I bought a bunch of basswood from MicroMark and proceed to first built the frame. I cut some 1/4" basswood to be 8" wide. I used the scraps I got from Jon to build a nice jig and quickly glued 4 frames in place.
Weight and clamps are used to make sure that everything dries flat. While these were drying I decided to make the gear mechanism for lowering the doors. It is only on the one side. I started with some pawl castings from Ozark and cut the gears out by grinding from behind.
A few scraps of styrene and NBW casting and I’ve got a reasonable facsimile.
I need 8 for my 4 cars
Bolsters are made from I beams. I sandwich a small piece of acrylic between the two beams, filing down the flanges to allow for a close fit. I stuck some NBW castings into 3/32" tubing to complete the look.
My order of basswood just arrived, so next step is to cut the side pieces to 9.6" wide. 
