Solar Panels: How many watts?

As Ed said, depends on how much power you draw. So there’s no way to hazard a guess without more information.

hedgehopper wrote:
How many watts of solar panels would I need to keep two 12-volt batteries charged? I don’t know the specs on the batteries. I’m looking for a ballpark number.

What about portable panels vs those mounted on the roof?

The answer to your question highly depends on how many amps you pull out of your batteries each day. For zero amps with battery not being used in storage I would suggest a minimum of 50 Watts for up to 200AH. Use a suitable charge controller with the solar panels.