This is not exactly what you are looking for, but many people have made their own upper cabinets (front and rear). Scamp
sells them fairly reasonably, but the shipping is very expensive because it is truck freight. There were also some files (maybe in our document center here) where people made dimensional sketches for Boler
says there are slight differences in the Scamp/Boler cabinets, and also now the rear of the Scamp is more square than the Bolers and older Scamps (like yours I believe). I think this is because they wanted to put in a "flat" rear window.
I'll search and see if I can post links to previous threads; there is a treasure trove of information available here in the archives that people have posted.
Scamp Upper Cabinets Questions
Roof Mounted Shelf/Cabinet
Less useful, but still might have some info for you:
wanted: upper cabinets
Start this one at post #85 (boler rear cabinet so not totally apropos):