Bumper leak! What to use and where to seal?

[dasher]

I have a leak along the rear back wall primarily on the street side of a 1999 Safari 25. I have been working my way down from the roof cleaning and sealing and I am at the bumper. I read so many posts about how to solve this leak from standing water on the bumper. Drill holes, remove the whole storage box, seal the bumper wrap, don't seal the bumper wrap, fabricate new flashing from aluminum.....

I have the bumper trim and wrap removed and I am cleaning all the old caulk and silicone that others tried before. I am confused as to how to prevent water from reaching the wood floor of the rear bedroom. I will be doing some minor floor replacement along the back corner but I want to stop the leak before I move to the interior.

Any words of wisdom are greatly appreciated.