The only design I've seen that may be similar to what you describe is when they use a molded front cap similar to what Thor used on 19G. On these it appears they shape the fiberglass (or whatever material they use) to fit up to Ford van roof similar to what was done on travel vans or Class Bs. In these the overhead bed area comes close to rain gutters on sides and windshield in front.
Is this similar to what you refer to?
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