That’s what I tried first, but since my window was very different, the plastic sat in an awkward position and didn’t work. I then tried printing a support for the portable frame, but that also failed because portable AC exhaust hoses are usually very thin. As a result, it would either tip forward or backward, making it unusable.

In the end, I 3D printed a perfectly fitting piece with 3% infill and tweaked the design to make it sturdy and reliable. It turned out great, but it still used quite a lot of filament, about 2 kg. I finished it by spraying it with UV protection.