What ESC are you running? If you're using an MMM, then don't worry too much about it as it's splash-proof (has a conformal coating over all the innards). Castle have said themselves that's it's perfectly safe to run it in wet conditions, but just don't submerge it. If you're running another ESC...well, you'd need to find out.
Your motor should also be fine if it's got a sealed can, as there's basically nowhere for water to get in. Even if water did get in, then the motor would still run absolutely fine (you can even run a BL motor submerged, though it's highly discouraged); you just don't want water in there all the time, as it's not good for the rotor/bearings. If you are running an open-can motor in the wet, make sure it's dried out after each race or even better, try and close up the holes. It'll make little difference to temps.
IMO, just keep a close eye on your batteries' balance taps and battery connections. The balance taps have a number of close-together contacts which could cause problems if they were shorted out by water, so just tape them over or whatever, and you should be fine.
