The problem with lead acid batteries is that the realistic usage is only 50%, if you pull them down past say 12.2 volts, you are doing real damage to the life cycle of the batteries. In battery tech, you get what you pay for. As an example, this battery: https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
Is significantly better than the 2 batteries you currently have, because it has about 1200 Watt Hours worth of capacity in it's 100 Amp Hour. You can take that battery down to say 10.5 volts and charge it all the way back up using your solar and an MPPT charge controller such as this: https://www.amazon.com/SmartSolar-MP...68&sr=8-3&th=1
Which that can handle all your 600 Watts and charge the above battery quickly.
So the question becomes, how would you use 1200 Watt/ Hour?
You could cook using a 1200 Watt electric stove for an hour.
You could run a hair dryer for an hour
You could run 12, 100 watt light bulbs, for an hour.
Even the best of battery tech, is somewhat limited in what you can do, and you still need an inverter to change the battery from 12volts dc to AC for your camper.
That's why I chose Goal Zero power stations because they include the higher end battery tech, with an inverter built in. Such as this: https://www.goalzero.com/shop/portab...r-station-app/
Again, I know expensive, but I wanted a portable out of the box solution. You could essentially build your own version of this using 3 of the batteries above and an inverter such as this: https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
PS, I used to think this kid was an idiot (couple of years ago), but he cleaned up his youtube feed and started doing amazing content for beginners in solar: https://www.youtube.com/user/errolprowse/videos
Watch all his videos to learn more.