Why not make the Kammback out of the rear window? Just make some spacers to git the right angle and then you could have it made of a more durable material so you could lock it.
2mm should be fine if you have good framing for it. Thin guages are good for just bending onto a curved shape, while thick guages, 4mm and up, are more suitable for holding a shape without a frame after heat-forming.
BamZipPow: I dont understand very well. Can you please send your vision ? Thank you
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Fiat Punto 1.1 12v 40 Kw -96', cd 0.31. Fuel scan gauge, smooth wheel covers, sealed headlights joints and surrounding gaps. Personal verified record - 4.3 l/100km on 105km trip used DFCO mode.