You are way overanalyzing this. Water between the cam and the pedestal is not important. Water between the housing and the cam is not important. You could take the cam (eyeball part only) and hose it down. The water will not invade the cam. You could place the wire from the cam into the box through the rubber grommet and hose it down, it will not make a difference. The water will not get to anything important.
You are worried about water sitting between two painted metal parts. Look at it this way: water runs down hill. If you mount the box on a soffit, it is hanging upside down. So is the cam. Any water that some how finds it's way between the cam and the pedestal (like you decide to hose it down) will flow right back out through the space between the housing and the cam. If you mount it on a wall, the same thing will happen. It is not just going to sit there and some how find it's way into the cam or the box. Water will not pass through metal. There is no seal between the pedestal and the faceplate of the box.
It is actually a smart design as there is no way/place for the water to pool and potentially rust the screws.
I have had several cams mounted from boxes from hardiplank covered beams and on the side of my house in full exposure to rain for about two years. No issues.