Rainjer,
It's already done for you - just take the relevant parts form the two profile downloads:
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Superleggera profile
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Trailer for Two profile
The back curve of the Superleggera is 44" long and the front curve of the Trailer for Two is 48" long, so a 10' trailer will have a 28" section of flat roof in the middle, while the 9' 6" trailer would have 22".
The profile drawings are all to the same scale so if you just want to see what your idea looks like, you can print them out and stick them together.
Andrew