House battery voltage under draw?

tommymsw wrote:

I didn't realize that plugging them in would be SO much better than driving...

... My hope was to run the generator or plug in at a park and only rely on the solar to keep the batteries topped off from normal drain while it sat empty in my driveway.

My generator pushes 40A I think and that sounds like that will also not be enough (Still working on getting it running).

So I guess the best thing would be solar. I have the 10W and that is clearly too small (wonder why it was even an option). I wonder if it is as simple as just putting a 100w panel where the 10w is? Or if I need an entire new system. Not sure if you need a different controller for a more powerful panel of if it will just charge quicker with the better panel.

Depending on your alternator and how it is wired, driving half a day can be better than plugging it in 20A overnight. Doesn't seem to be the case with your bus, though.

10W solar is small, but not terribly small to maintain 2*6V batteries from discharging.
Really bad 200AH bank could self-discharge 1AH a day.
10W solar could harvest up to 2AH a day, often it will be less, still it doesn't look like it absolutely can't maintain 200AH bank.

But there can be devices in your bus that are always ON, you didn't investigate this. Then there is more draw than self-discharge. How much more, you don't know. Replace 10W panel with 25W and if there is no controller of any kind installed, or it's smaller than 3A, - install some 3A-4A controller. They probably don't come smaller than 5A.