The two trailers have had a little bit of filler applied to the roof joints, followed by a coat of primer. After removing any rough bits that showed up, another light coat of primer was followed by a coat of bright red (as a good base colour for the train red that will be brush-painted on afterwards.

What this photo also showed up more obviously than before is that the side panel closest to the camera is not straight and needs to be removed and remounted. This demonstrates that taking progress pictures is not only for my own ego in showing off the models, but also a useful tool to show up any little errors or omissions before it's too late to fix them.