VR,
I will keep looking for the outlet plug combination I tried to describe, but I have not found anything like it at any of the boat stores I have tried. The main brand of such things that all boat stores seem to have, is Marinco, and they don't have anything.

Don't be too impressed about the "rain cover". It's just a square of fabric large enough to fold down the sides of the box, neatly folded at the corners (like hospital corners on a bedsheet), held in place by the nylon straps that tightly clamp the box to the rack. One corner is not folded and tucked; it forms a tail of sorts that covers the plug. I have ridden in some pretty serious downpours with no problem.