I couldn´t find any 3D printable models for the GP5 filter so i created my own one.
The bottom part (bot) clips into the top part after printing.

The top part should be printed with the thread pointing up.
The bottom part should be printed so that the outside fold sticks up.

After printing the bottom part might not fit that tightly since it is sized to fit after painting.
However it should still hold even without paint.
If you want it really tight you can print a test fit and scale the bottom part up by a tiny amount.

I recommend using an adaptive layer height for good and fast results.
Both parts need support structures to print propperly but any part that needs support will not be visible once assembled so you can use very little support.
A brim is pretty much needed for both parts
Infill can be really low. I used 3% infill.