Connecting 2 banks to one controller?

[Scubatony]

I have a Prostar 30 amp charge controller connected to 2 135 watt panels. My current house bank is 3 group 27s flooded. System works great and I also have wind generator on the same bank. I will likely be adding another 200 watts of panels in the near future.
My desire is to go all solar so I am dumping the Infernal combustion dingy motor for an electric trolling motor. Speed is not an issue for me. I am going to get a 4th group 27 battery specifically for this purpose.
My question to the learned audience here:
What is the best way to charge this 4th battery from my solar array? I am told is not good to hook another battery of uneven voltage into the main bank. Do they make charge controllers that can handle 2 banks? Or should I put in a switch that flops the controller between the 2 banks just when I need to charge my dingy Battery?
Thanks in advance.

ST