I flew in down pour once. I had just hand launched my 1/2 Sure Flite Cessna with a TD051 engine and a 2 oz. tank, good for about 16 minutes. No sooner had the plane left my hand when the sky opened up. I ran for cover and stood under a covered walkway. With no throttle control I really had no choice but to keep flying. It flew pretty good for about 8 or 9 minutes and finally the rain was so hard that the engine started loosing power and I was able to belly in.

I also saw the same thing happen to a friend one time. BUt there was a severe gust front. The plane flew backwards away from us until we couldn't see it anymore. We spent hours looking for it. Found it over a mile away on the other side of an interstate.

I personally worry about water getting into the xmitter.

I did fly float planes for a few years. And they get wet now and then. The fuselages tend to warp, turn into bananas after a while.