There are more models in HO for 3d printing than O. Getting the scaling right may take a few tries. I was able to use an HO design for a circus trailer scale it up and have a new circus trailer, one I can put the animal in. The K-line trailers are glued shut. See the comments for what I did for the White Circus Trailer.
Next major 3d project, TANK engine using early 2026 drive train. The one with the smoke flapper driven by an internal cam on a wheel. Makes a self contained unit. It may be a few months getting it all together.