Most of us over here race in the rain, but most have a special rain car, since you need a completely different setup in the wet.
It's correct that the receivers are packed in a balloon or condom to keep them dry. I have vaseline in a spray can which I spray on sensitive areas like the servo cases, switches and bearings.
You have to dry the car thouroughly after a wet race, an air compressor is a must.
Once all this is done and you have diffs in the car and good rain tires, it's a blast to race in the rain