Lead acid batteries seem to be pretty forgiving when you connect them in parallel.
With solar power, you want to make sure you are using as little power as necessary, since power costs a lot to generate. Conservation is the most cost effective approach. How well are your pontoons designed? are they really just rectangular blocks? How fast does it really need to move? Could you reduce speed a little bit and reduce power consumption a lot?
We used solar power for our
underwater ROV for the NURC this year....good stuff....