I found out fifty years ago that water rusts bikes :lol: that's why mine has only been washed 5/6 times in the ten years I have had it
if it gets mucky it gets a gentle wipe so as not to let the muck do a lot of scratching and then lathered in WD40 trying to avoid the tyres and brakes
To be honest though I don't do off road and these days I try to pick the best weather, seen plenty off crap weather in earlier times.