I got inspired by the passthrough part, but was missing the option for having a bowden fitting placed in the passthough - and a cap, that could be mounted with the bowden fitting sitting inside the cap.
This is what I came up with.

The printer need to be good calibrated in order for the threads to be printed in the right dimensions. Make sure, that extruder e-steps and extrusion multiplier is set correctly.

Early version of the files had the thread for the cap as M14x1.0 - this has been changed in the current version to M14x1.5, as this is easier to print and to mount afterwards.

These are the fittings, that I use in my model. They are often labeled as M10, but usually it is 1/8 NPT thread (I found M10 thread to be a bit loose).