Well, both the enclosures look nice

Actually I know some people keeping the snakes in an enclosure with a lot of water. They have a filter and they refresh the complete water often, they don't keep fish in it though ( I also suspect that you can never keep fish long together with garters ). But they make sure that they have a also a nice and always dry area the snakes can lay on. Also they have very good ventilation.

I think you can still use your set-up ( larger water part ), but just need some small adjustments ( land part little bigger and very, very good ventilation without it becoming a draft ).