The curved roof for the shepherds van was a very different profile to the top of the ends. Fortunately, resin can be softened by hot water, so it took a bath in the sink.
After a few minutes, the material had softened and could be flattened by massaging it with my fingers. This took out most of the curve.
After this, some nice thick blobs of epoxy and a few clamps made it fit. I suppose I could have gone straight for the clamps but making at least a token effort to re-shape the part does seem the proper way to work. And I always like to do things properly!