This discussion in a nutshell:
Here's my solution for connectors that need to be installed and tested once, and then stay connected all the time:
Double row headers. At the male side, one can move the pins around until everything fits correctly should the need arise. To make them watertight, I put a bit of hot glue on the cables and solder joints before shrinking them in. Then I add a bit of vaseline to the contacts before connecting them. Finally, I put a 1.5cm long additional piece of shrink tube over the gap where the connector mates to make the connection permanent. I can cut open the shrink tube to disconnect the connector, and I can remove the idividual side's shrink tubes and even solder through the hot glue to remove individual cables if I want.
An even better alternative to double row headers might be Sub-D connectors:
When one drills through the holes of the metal case, the two halves fall away, and just the plastic part with the contacts is left over. The size is now much more manageable. If one needs not all 9 contacts, the excess part of the plastic and contacts can be clipped off.
For permanent power connections, I take 3.5mm bullet connectors:
They cost next to nothing, and can carry 50A no problem.