I leave mine on in all weathers, and rain etc. has never caused a problem.
Really pleased with it. The battery seems to last for days and days in ordinary use, though I don't often listen to music. The only slight irritation is that GPS over-rides the intercom so conversations keep getting interrupted on complex routes. The radio is fine but I don't get very good reception from weak stations; maybe the antenna isn't routed ideally. Worth considering.