I'm especially interested because I think I may have a similar issue.
I know now that I have 2 overfill tubes on the non-door side of my Toyhauler. They are in the access for the black tank and gray tank1 shutoff valves. I attached hose extensions to these 2 overfill tubes to direct any water down below the frame and coroplast. So, when I fill my fresh water tanks, I watch these overfill tubes for my signal to shut off the water fill. At the first sign of water, I stop filling the tanks. And the water that comes out of these two tubes is directed out below the campers frame, BUT I will then have water start pouring out by the hydraulic leg just behind the door, on the door side of the camper. This water is running out of the coroplast. The only time I have this water running out (and it will probably run out for about 10 minutes or so) of the coroplast by the middle hydraulic leg is when I fill the fresh water tanks. It would make sense if there were two more overfill tubes up above the coroplast, although I don't understand why there would be more than 2 overfill tubes for the two tanks.