In my mind, keeping water out and dry inside is easy, get good 'breathable' rain gear and use it.  If it gets too warm portaging or whatever, unzip the vents and it's all good. but in reality the last 2 years has been like walking a tightrope trying to stay dry.  Last year i sweat profusely on a portage with no way to stay dry.  Under the rain gear all 'quick dry' non absorbent clothes.  then the temp dropped and it's a wet cold paddle to make camp.   i wonder if in those conditions it would be good to have something non-absorbent next to the skin and in addition, something sacrificially absorbent just under the rain-gear that can come off before hitting the water.
5 years ago i used a pair of something like frog toggs (dift brand, not as thick, don't recall the name).  about 20.00 for pants and jacket, advertised 'breathable'.  That trip it rained a lot for about 4 days.  I stayed very dry and comfortable in that set of gear with no pass thru pockets and zippered pant bottoms. It was overall warmer than most rainy June trips.  Durability may be an issue, but that stuff handled the water well.  Cliff Jacobson mentions using 2 rain jackets at times, one under his pfd and if necessary, one over. ugh. rambling on...