Re: float (maintenance) charge without a charge controller
Yes, you can. I would install a "blocking diode" and a ~5 amp fuse for safety.
Is this an AGM bank or a Flooded Cell battery bank?
You should monitor the bank for state of charge. Flooded Cell batteries tend to have higher self discharge and as they age, the self discharge rate goes up...
You may find you will need closer to 240-1,000 watts of solar panels to properly keep the bank charged due to self discharge (depending on brand/model/age/current state of the batteries).
At that power level, you may as well look at a "real charge controller" (PWM or MPPT type) to insure that you do not over charge them either (AGM's do not take well to overcharging).
If the batteries have been sitting for awhile--You should check their current state of charge and get them on an AC charge controller if they are below 80% stage of charge.
20x BP 4175B panels (replacement) + Xantrex GT 3.3 inverter for 3kW Grid Tied system + Honda eu2000i Inverter/Generator for emergency backup.