This Bumper has an extended area around the perimeter so when fully open it supports the screen from flex because of the camera bump.

Printed in ASA was the best for me, but choose whatever filament you like.  Did not try TPU so don't know how well it would fit. Painting supports on the ends will keep the curved end shape better.  Will need double sided tape to stick to the Duo.

https://www.amazon.com/gp/product/B019OQ4ZG0/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1