First, you may buy Mtroniks waterproof ESC, then life is getting easier. Second, a raincover from Slipstream.co.uk.
Get Dunlop D20 tires or some foam rain tires.
Setup, caster to 1degree front and rear, toe out 0.5, roll center high, tie rods second hole from inside. Front kick-up 4 degrees. Rear anti dive 0.