Got a vintage caravan with a Trimatic door that has gone all wobbly?
You need new corner inserts.
It's easy enough to buy them for $10 AUD per corner, or you could just print a few of these.
Recommend to print in PETG or ABS. There were specifically designed to replace the inner screen door corner inserts with aluminium extrusion internal dimensions 29mm x 16mm.

The original inserts are 2 piece that clip together before inserting into the door extrusions.
I gave this concept a go but it is over-complicated and doesn't offer much more than a simple single piece print with some infill.
Photo of original, 2 piece insert for reference. I have seen a few different modern replacement styles. These ones are the original 1970s item.