I created this window vent to fit my L300/Delica 1990 4WD. It protects from rain and mosquitos and still have some fresh air at night.

This design needs six prints (1x frame & 5x slat) and roughly 700g filament per side.

I used a Creality CR-10 S5, which officially has an 500x500 bed size, but in reality it's 510x510, which you need to print the frame in one piece.
To utilize every mm of bed size, you'll need to play a bit with the bed size settings in your slicer.
(You could also print this on smaller printers in sections and glue back together. You would need to adjust the geometry then.)

I printed all pieces with a 0.8mm nozzle, as detail is not really important, the speed advantage is super helpful though.
I used PETG for now, but don't think it will withstand direct sunlight, so i'll need to test some more filaments in summer. Assuming ASA would be the best, but tricky to print on a printer that size.

Once you printed the 6 pieces, you need to glue the slats into the frame.

To keep mosquitos outside, just use some mosquito net and glue this to the inside.

You can then slide the vent into the rear folds of the side window's sealings. You should fixate it there with some silicone.