Finished and printed the first design of the rain collector pouch cap. It’s two parts: one that presses against the top of the opening with an o-ring and another that screws onto the pouch’s threaded mouth, which presses onto the first part as it is tightened.
This assembly was designed in Fusion 360 rather than OpenSCAD so I could design it quickly. Designing multiple parts that are dependent on each other can be significantly easier using Fusion360 than it is with OpenSCAD, though OpenSCAD has its advantages.
The threads were made by creating a helix and then sweeping an area through the path of the helix. It added some twisting but prints and fits just fine in both ABS and HIPS.