they don't need sealing really as the damp has plenty of other places to get in!!!....................
It's not the four screws that hold the box together, but the terminal screws that I am concerned about. Granted, water can still possibly find its way in through the point throw lever or rod, but there's not much that can be done there. And the amount of water getting in at those two points would be minimal, unless the switch machine is sitting in a pool of water. But the terminal screws are in a perfect place for water that happens to sit on the machine, not to mention heavy rains that could conceivably drive water into them. The other six screws on the supplementary switch are in the same situation.
One other place, which I did not mention, is the joint where the supplementary switch joins the main body of the switch machine. I think it too should be considered when talking about waterproofing these machines.
I don't believe that the entire mechanism should be sealed in a bubble. Number one, it can't be done. Number two, and most important, any water that does get in should have a way out. That is why I am only considering sealing the top openings.