A 1986 Trinity model - pretty much like the above, frameless, sloped on the bottom. Unlike the above, the top also slopes toward the middle, so it appears the whole car "sags" in the middle. General purpose.
https://archive.atlasrr.com/NFreight/arc-n25500tankcar.htm

A mid 1960s General American car that appears to be frameless but without sloping.
https://archive.atlasrr.com/NFreight/arc-n20ktanker.htm

What have you planned next?

Tank cars would fill a gap in your lineup.

An early 1950s model with dome like this General American - I particularly like the platform around the dome. (versions without it go back into the 1940s) Pretty sure it is 36 feet long. This era also had a lot of colorful paint schemes.
https://www.tangentscalemodels.com/general-american-1952-design-8000-gallon-welded-general-service-tank-car/

A 1969 ACF model - it has no underframe - so the structural integrity comes from the tank itself. The bottom middle of the car is sloped from the ends to allow the load to run out of the bottom valve in the middle of the car. Used for oil, bitumen, fuels. Also used to haul food oils, alcohols, various chemicals etc. A very general purpose car.
https://archive.atlasrr.com/NFreight/arc-n235ktankcar.htm

What 53' and 48' containers are you using in your images here?