When time allows, I will be cleaning up my plumbing inside the water panel. I agree the plumbing was poorly thought out, at best. I won't use a manifold, as that normally would be home runs to each fixture. I am sure it could be done, but I don't think you would really lessen issues with RV plumbing, by doing it.
This is what mine looked like before I cleaned up the wiring mess:
With the panel on, I could not physically touch the low point drains, until I did the clean up.
This is the current state after: