I wouldn't try to create a waterproof compartment; mainly because I doubt you will be 100% successful attempting this post production if that makes sense. What is more likely to occur should you do this, is that you will create an almost perfect compartment that effectively traps water (even small amounts trapped in there will create havoc) in with the powertrain.
I agree conformal coating is a solid choice; it's what I used in seattle on my FPV drones to great effect. This will also help prevent oxidation on your electrical contact points. Someone mentioned that the wires can present significant challenges to any proofing method; they often are. I think you can mitigate this by applying diaelectric grease to the the junctions or where they connect. Pretty sure water hates it... this also helps keep your electrical connections oxide free. Plus the humidity you mentioned is always going to be attacking those contact points no matter what method you choose minus the han solo freeze for the entire compartment.
The Boosted Rev was one of the few well engineered frames available. By that i mean that water proofing/resistance measures are most effective and easier to implement when built into the design vs retroactively. My Boosted Rev was a dream when it came to water/snow. I Used to take it into the diy car washes, and just have at it with the pressure washer, never an issue. The Rev's compartment had intentional openings on top of the deck and on the bottom. Their design team focused on sealing the cables, ESC and battery vs the compartment. Granted the Rev has other shortcomings, but there too was a fix I recently got. Provided by a company in San Francisco, WingMods. Let me tell you this thing can boogey; so much so that I am going to be reverting to the OEM power train here for the winter. Way to much torque for snow/ice situations. Even with grip studs in place I wouldn't try it. I am getting off point.... so this he aftermarket battery and ESC i have are not truly water proof. The Stormcore ESC less so. I applied conformal to it, and so far no issues. THe battery like many escooters is generally sealed but I would not push my luck with it if I am able to. However the solution I found that has worked so far is separate from the Rev entirely...
Those motorcycle dryers on Amazon... Looks like an electric teapot kinda, and you just basically go over the scooter anytime its damp/wet. Takes me literally like 45 seconds to basically blow off every last trace of moisture on it (dirt, leaves etc too) Plus you get the benefit of preventing scratches from hand drying. They run about 100 bucks, which is kinda steep, but it will keep your ride nicer longer so depending on your EV investment this may or may not make sense to do.
This is starting to look like a wall of text... sorry... in closing, the only other thing i can think of would be for the battery specifically. You can order multiple sizes of the shrink tube on Amazon. and then basically shrink wrap the existing pack , then do it again but alternating the tube sizes so as to basically have them flip flop the second time which creates a good seal. Micha on Youtube , he has a channel ebike school where he discusses some do's and don'ts for DIY battery packs. This method i mentioned is demonstrated in the video, because i know i did a poor job explaining this method
Best of luck to you my friend. Hopefully someday all scooters will be like most ebikes out there; a general industry standard of water resistance that is more or less effective against rain, splashes etc...
