And even some commercial ones aren't. When we bought out box's the divider was at the bottom where it would sit on the deck level. I moved it to the top and then have the PVC pipe coming up above the lower part of the divider that is in the middle. Never had any rain or green water enter at anytime. I think the Lin and Larry have pics in one of their books on the layout.

Go Slow
Sail Far
Stay Long