Why stop at rain? there's also the beach, mud flats and my personal favourite the river bank. As long as the truck/buggy is sufficiently water resistant and I am willing to tear down the entire car to make sure it doesnt rust away in the corner during storage.
I use 'throw away' electonics like a decent receiver and stock motors/nimh batteries which are completely sealed up. Yeah, the electrics might operate at a higher temperature but thats the price i pay for wanting to play in wet, muddy, seawater conditions. If something does indeed gets fried and shorts circuit, it'll add up to the fun.
My old Tamiya Hornet been a submarine and ATV all these while but I wouldnt tackle those same terrain with my race cars