used to commute so I used to ride in the rain. now I prefer foul weather of the frozen sort. the big challenge I remember used to be the rear rack trunk bag. I eventually resorted to using a big ugly thick plastic compactor bag (out of desperation). I just put the whole trunk in the bag, then lashed it to the rack. albeit this was for the torrential downpours. now for wet sloppy rides I use a simple rain cover. of course combined with the obligatory "waterproof" trunk & fenders
& having used barmitts this fall & winter, I'll bet they would be helpful in heavy rain as well. but they might need a drain hole in the bottom?
this trunk can actually be used as a beer cooler
