In my campervan I have 2 solar array arrangements.

Both charge my 12v house batteries.
One system is a 24v array, 500w MPPT controller.
Second system is 12v array, 250 watt MPPT controller.

Is it possible to connect an additional PWM controller directly to the 2v array and the 24v start batteries to keep them on float charge.

I have tried a succession of buck/boost chargers on the 12v array, but they have not been up to the job.

With thanks.

Robin