I've wondered about your exact line of thought. When I see these trailers torn down to the bare metal frame in a complete frame-off restoration I think it's not too far from building a brand new trailer. Which sort of appeals to me (but definitely *not* my DH)
Another way would be to snatch the biggest squarely-shot google image of the trailer you want to copy and resize it in photoshop, using the ruler function on the edges of the pics like graph paper. Or a good, squarely-shot pic from someone's blog of a newly-completed wall frame.