good question WSB
I too would like to hear what someone with more knowledge than me has to say abuot this.
Off the top of my head I would say just make sure the cover plate is sealed good where it bolts on and make sure the bolts have a good seal. Other than that I really don't know for sure.
I ride in the rain alot....I use a little RTV around the mag & clutch cover to keep water out. Also some over the electrical connecters. I use fender's on my bike and that does help keep water off the motor.
I have had no problem's riding in the rain..just don't go splashing in puddles of water like you are in a swamp buggy race..do your best to keep water away from the carb so you don't suck it in. I alway's lube my chain and check my wheel bearing's after a good soaking.
I also use a little RTV on the CDI, especialy were the plug wire goes in...
Watch out for "Splashers" you know...the ones that make a game out of trying to splash you with water when they pass you....They will