Well Im trying to figure out some last minute things for my tour (well the tours still in 2 months, but im a planner

). Its going to be down the Pacific Coast. Unfortunantly, the only time I can fit it into my schedule this year is starting in mid-May, and going into June. I know its going to be a bit rainier that time of the year, but thats not going to stop me.
My biggest concern is keeping my gear dry on this tour. I have a down sleeping bag, and if it gets real wet its pretty much useless. I tour ultralight, so my only carrying system is a large dry bag on the rear rack and a large handlebar bag. The dry bag doesnt let stuff breath through it, so for example lets say my down bag and one of my shirts are wet. I cant really put them in the dry bag because they wont dry in there, and I cant strap them outside because its raining, what would I do in this scenario?
Thanks guys