There are a few alloys of silicone that you could use as a non-conductive inert and waterproof coating. Sadly, they're not particularly cheap, but they do serve. I've used Dow-Corning type 734 for a number of applications, including this one, with success.

My experience has only used lower voltages, i.e. 3V3 to unregulated 10 volts. Lab experience (other folks' labs) have taught me that voltages above 28 volts are to be avoided. That was, in the past for reasons mostly associated with fire and sparking, but the higher the voltage, the better the insulation has to be.

With a careful application, the type 734 sealant (there are competing products, but read and understand the spec's) can be applied in a way to make a common membrane keypad quite waterproof. The clear version, which is what I've used, is translucent and, applied very thin, can be quite transparent, certainly enough to read labels larger than 10 point type.

It's not expensive enough to prevent a few trials, BTW.

RE