Piano hinges leak. They leak even worse when dragged through water. (same goes for speeding down the interstate in a rainstorm) You can cover them with neoprene, or Naugahyde, or You might consider a gear hinge for your TD cabin doors SoCalTearDrops sells those. Not cheap at $20 a foot, but my neighbor is still happy with it. http://socalteardrops.com/hinge.html
The bottom edge of our TD cabin doors are about 6" up from the bottom of the sides, (the sides overhang the frame, which I might not do again, actually) so the water has to get that much higher before it gets inside the cabin. In my experience, water dries out, so even if we get a little wet, we're usually in a desert anyway. If we traveled to more humid areas, I might think about it differently.
I used the same aluminum on the bottom of the TD as we used on the sides. The idea being to try & protect it the bottom, not just leave it as bare wood. I'm going to go around the bottom & reseal it with silicone too.