I will take some pics tommorrow to add to this post...but I notice something as I was walking out and it didn't hit me until I was on the road home.
The aluminum bumper goes all the way across the back and there was a lot of rot at that joint between the top of the bumper and the wood frame. What I noticed was a L-shaped lip about 1/2" legs where the bumper hit the wood. A water trap waiting to happen. And it did!
My proposal will be to remove that lip from the top of the bumper and seat the bumper top directly to the bottom of the wood frame. But there will be a galvanized flashing installed on the wood first going under the frame and up the back to be covered by new siding. The gap between the bumper and the new outside covering will be visible, so cover that with a trim strip, I am thinking a mastic attached trim...no need to be screwed on every 8"...and if screws are needed into the bumper as to not compromise the flashing under the new surface material.
Any more ideas will be appreciated.