Advise needed for on board charger

I am wanting to ad an on board charger to system.
Currently have 5 group 27 batteries.
1 battery for boat electronics/starting.
4 baterries for stereo. 2 (Parallel) A... seperated by perko (2 more Parallel) B..... or.... ALL
Setup with 200 amp relay to connect the 1 battery for start/electronics. to either A or B for charging when on water.

Question? If I get a prosport 20 3 bank will it work? And would it be hooked up? One lead goes to start, one lead to 2 batteries A and one lead to 2 batteries B?

Hope I didnt loose you in the explanation of setup

Is prosport 20 the charger that is best for this, or is there something better?

Thanks again