Looking at some
hybrid D sub connectors at RS atm. They would be good to carry power and signals. I don't think they have any sealing rating though as you select an insert the power pins you want. I'll look at digikey some more.
edit:
also looking at sealed (IP68)
USB connectors element14...but they all appear to have rather large mounting diameters, like the Altronics version. We would have trouble with the case size and the connector size.