That is a really neat idea. As I was reading I kept looking over at my 36 FOWLR
bowfront. What I would do, since plexiglass will get scratched and beat in a saltwater system...I would get a piece of something more durable, say acrylic, and go from a bow to...well, whatever shape a bow with corners has on it. This will allow you to create the wall you were talking about to strengthen and provide longevity to the plexiglass sides and then have a viewing window that will provide what it is you are looking for. Infact, I would actually recommend acrylic since it is clearer than normal glass and it would probably bond easier to the plexiglass, just not sure about that.
This is a really cool idea. You are turning a 28 gal
into a 20 gal
nano with internal fuge. The best part is this will actually be able to be a good fuge for exporting nutrients. The small ones usually don't work to the best of their ability.
My only other suggestion would be to maybe work with one return pump rather than 2 and if you are wanting more flow for the fuge then you could add a powerhead. That might make things a tad more simple from my viewpoint.