I decided to build the entire interior so that I could practice that on this car. As mentioned before, my intent is to install a coal load so none of this will be visible. The whole idea behind the interior is to make sure that when the doors open all of the coal slides out of the bottom. Everything inside is geared toward guiding the coal toward the doors. The main divider over the car's center sill was the first thing I tackled. There are several angles which are hard to measure on the built model. Some trial-and-error was necessary to come up with the final shape and size. I used the calipers to measure the width of the center sill on the model. I then cut two strips of styrene to be 18" wide and the length of the model (note that there is a central, vertical sheet in the middle of the car, so what you see in this photo has to be built twice. Next, I lined up some weights to the width that I had measured, put a thin strip of masking tape over the two pieces of styrene, and folded them as shown in the photo. I could then apply glue to the seem.
I put the car as I had built it so far on the scale and it weighed 3.5oz. A car this size should weigh about 6oz, so I am still 2.5oz short. I decided that this divider is a great place to hide some more lead shot. I am supergluing the lead shot in one of them while I'm waiting on the other divider's glue to dry.
After some more tweaking and removing some individual lead shot, I kinda, sorta got the dividers to fit. Again, not perfect, but good enough for now since the interior will be hidden later on. I glued the dividers in place with 5-minute epoxy. As you can see now (or rather not see now), the center main brake line brass wire is completely hidden in the final model, so that is one piece to just ignore on future models. The more I stare at prototype photos, the more I noticed that they used strips of metal to cover the joined areas of the sheets, which I can duplicate to hide the gaps that are visible from above. Something to consider on a future model, should I want to expose the interior.
Next, I formed and installed some sheets to represent "tunnel ice-breakers". In the prototype these were installed later in the life of the H21a cars, and not all of them had it, but so many of the prototype photos I see have them that I decided to include them.
The very visible cross bearers were formed from four angles (Evergreen Scale Models part #291). I first glued two of these angles back-to-back, and then did another set like that. Then I glued the two sets back-to-back to form the cross section shown on the right in the photo below. The prototype uses a slightly different (and more difficult-to-duplicate) shape, but this one will do for now.
This next photo shows these being installed after I trimmed them to length. One side of my car is slightly bowed out, so I used the clamp to hold the center one in place while its glue was setting. Not much pressure is applied; just enough to hold the part in place. There are five of these cross bearers, so two more to go. This is about it for the interior. The rest of the work will be adding details to the outside of the car.