The question of using a TPU seal for waterproofing has come up multiple times already.
The OBS MainCase currently has a whole bunch of openings that are not waterproof:
This is about coming up with a solution for waterproofing - for instance TPU seals - Individual issues can be created by individuals working on the different openings.
As currently there are no reports of Water damage being a major issue this is mostly a "nice-to-have". Some people would like to - at least at home - be able to leave their OBS on their bike even in humid weather conditions.
forum thread about the topic