[Sedri]

I've had great luck with actually coating the esc circuit board completely with a high quality/high temerature clear silicone sealant that normal people would use to seal around windows or around the bathtub.

You can buy a squeeze tube at the local hardware store, strip the esc down to the circuit board, and carefully coat the board top and bottom (sqeezing the tube and squishing the silicone down bewteen and around everything - wear latex gloves!), being careful to also seal around the ends of all the wires where they are soldered to the board. Don't cover the heat sink, of course, just get the silicone underneath to seal the connections there. If you beat on your car pretty hard, ESC temps might possibly be higher, but I don't know from experience because I always undergear my cars a couple of teeth just to remove the worry of overheating.

Batteries? Fine Design (just for example) sells "marine" Lipo packs (3700maH, 4S1P packs) that are fully waterproofed from the factory, but why not just slip your pack into a "balloon" and zip tie around the wires?

Servos? I run Futaba S9304 coreless servos, which Futaba lists as "water resistant", but I routinely wash mine off under running water with soap in the kitchen sink, and I have never had one leak a drop. Four years old, and they work like new - an excellent investment and peace of mind, even when driving in the rain, which I've done a few times!

As for the motor itself, I haven't figured out the best way. Some people just make sure the rear endbell is clean, then cut a square piece of good quality electrical tape (which is rubberized, by the way) and put the square of tape over the rear bearing area. That way, you can EASILY and very cheaply check and replace this "cover", and it's foolproof for a quick romp in the snow. As for where the wires go into/through the motor (if you don't have a Lehner with the brass tubes, that is) RTV sealant, just enough to seal that area, seems to work great. The only problem left is the front endbell/output shaft if you use an endbell mount. I use canclamp mounts, so this is no problem for my motor. Simply another trip to the hardware store, ask where the plastic table-leg/chair-leg end caps are, and look for one that will slide snugly over the end of your motor (typically 36mm for "540" sized motors)

You will only need to drill a hole in the center for the output shaft, and the plastic caps conveniently have a dimple right in the center already, so it's super easy to put a hole in the center. This won't be 100% waterproof - you can't drive it underwater - BUT, in my Landmax Rally, which I've driven in the rain, through puddles, in the snow and generally everywhere, my only contamination problems have been with seizing and/or rusting wheelbearings - and those were rubber-sealed bearings, no less! Water was running off of everything after my most fun drive in the snow; you'd think that I had driven my car through the car wash!

Good luck!