When we sprayed the bike seat with the hose last week, water seeped in to the stashbox, which is a no-go for people riding in the rain. So yesterday we spent the day trying out several different gaskets to make sure water can't get in to the stashbox.
We ripped off the gasket the factory made (it looked like engine gasket material, way too hard for what we need), and bought some weather-stripping from the hardware store. The first iteration was a tubing-type of gasket material, much softer than the factory gasket. Results from the hose test = failure (though it was better than the factory gasket).
Results from the day: Now we've got a design that we will send back to the factory to modify the gasket and keep the stashbox dry. We also really like the look of the white gasket with the black color of the bike seat frame and cushion and are going to have the factory include that as well!