I decided to build the side walls first, since they appear to be the simplest to construct. I am building them using strip wood. I think that is going to yield the best match to what the prototype did, with the natural gap between the boards duplicating the indentations between the slats. This photo shows my set-up. The side wall is 8'2" tall, so I cut a bunch of 3"x3" scale strip wood to a length of 10 feet. The body is just under 25' long, but I cut enough boards to make about a 27' wall. The boards are pushed up against a straight metal bar, and then two 90-degree gauges are used to make sure the boards are all perpendicular to that bar. After placing all the boards on the glass plate that I am building it on, I started slowly pushing them together. Since they will want to pop up, I put two metal weights on them. When the boards are very close to each other, they will want to push out, so I also put some weights on the gauges.
I am building the wall face-down, so that you are looking at the back (or interior) of the wall. That way the outside face of the wall is guaranteed to be flat on the glass plate. With the metal weights in position, I glued two long 3"x4" boards to the top and bottom of the wall (the 4" side is glued). Only a very small amount of yellow carpenter's glue is needed here, because this glue can stain the wood. By gluing the boards on the top and bottom edges, it keeps the 8'2" section of the wall clear.
(sorry for the blurry photo) Next is the marking of the top and bottom of the final wall. I made absolutely sure that the metal ruler is perpendicular to the boards, and then traced a pencil line at the top, and then another one 8'2" below that for the bottom, in the same manner as shown in this set-up. Note the white styrene strips. These make sure that the ruler is perfectly even with the metal bar the top of the photo.
I could then start to glue more 3"x4" boards horizontally on to the vertical exterior boards. When a handful of them were done, I could saw the top scrap off. The windows are 26" from the top of the wall, so I stopped when I had reached that dimension.
Next, I found the center point of the wall, horizontally, and from there marked out where the two windows are. Then, I could place a single board below the bottom of the windows. I let that one dry first, so that it was guaranteed to be perfectly horizontal.
After that, it was just a matter of gluing up more of the 3"x4" boards to fill the rest of the wall, and then trim the bottom of the wall so that the final height of 8'2" was established.
Next, I used a sharp knife and cut out the boards (from the back/interior) that make the window. The horizontal spaces between and surrounding the windows (on the back) was also filled in with 3"x4" boards (not shown). Some final filing will need to be done eventually. I am also leaving the walls long, so that I have some flexibility when it comes time to attach this to the end walls.
I built another side wall in the same manner as the first one. Again, the windows still need to be trimmed, and the width of the walls will get adjusted when it is time to assemble the body.
Since I forgot to take a photo of the completed back of the side walls (the interior side), I have added this photo. Note also that none of the sides walls in these photos have been sanded yet either. That will happen soon.