Regarding Scamp and Casita...
They are two different companies, each using their own frame and molds, which are not interchangeable. Some smaller parts likely are - don't know about the door hinges. You might be able to look at their websites and see. You could also ask on this forum as a specific question in a separate thread - I'm sure there's someone who knows.
There is a loose historical connection between Scamp and Casita. When the Boler
company in Canada folded, two different people started companies to produce a similar design in the US. Scamp got the molds. Casita made new molds and incorporated some changes. The two companies have each gone their own way since. However, the basic concepts are still similar and derive from Boler
: two-piece, single wall shell joined horizontally at the "belly-band", molded interior cabinets riveted to the shell, dropped floor frame with torsion axle
Other makes, Burro
being the most common, used a different concept: outer and inner shells joined vertically (across the top), with interior cabinets molded into the inner shell.
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