I bought one of the ones in the initial link. Mine is not especiall water proof, but a soaking with ACF 50 and location under my seat seems to do the job. I had planned to fit to my GS before it got wrecked, but since wired it to the Ural. It works fine.
Since then I have bought some brass body socketś of the same style: about £2 from the local hardware store. I have drilled holes in the sidecar body and mounted these. Yet to wire them in but I will then have another two power points in the chair....
One last one drilled into the instrument assembly for a low draw GPS plug and it'll be done.
Biuld your own, or buy one. They are not expensive if you hunt around on the net a bit.
Worth having even if you barely ever use them....
Adventure: it's an experience, not a style!
(so ride what you like, but ride it somewhere new!)