This dual-part enclosure is made for heating elements with a 38 mm hexagonal fixing nut (typically 1 inch / DN25 thread).

The enclosure is designed to keep potential water leaks out of the electrical connection part, as long as the heating element is mounted vertically. 

The cable inlet is designed for an off-the shelve M20 1.5 threaded passthrough inlet.

I used it in a self-made  flowthrough heater to dump my excess solar energy (when prices are negative). See last picture. Circulation pump not shown in the picture.

The model is designed in cadquery. Source code can be made available on demand (needs some cleanup, therefore not published)

Printing instructions: the top part needs to be printed with full support enabled.

ATTENTION: my goal is to warm the water up to a limited temperature. The temperature at the bottom (inlet) will be around 40°C  Please make sure your heater is equiped with proper protection against excessive temperatures.  Proper earthing is equally important.

I printed this in PETG as PETG should withstand higher temperatures than PLA.