As stated before, "solar ready" generally means that the manufacturer has pre-wired from the roof to the battery compartment. However, that may only be for a small panel and not for 1200 watts worth of panels.
If you want to add a solar panel, I would get at least 100W of panel. When it comes to solar, bigger is better for many reasons - among those reasons is that the panel will be flat and lose efficiency, rainy days will also be less efficient, etc.
The next question is whether or not they included a solar controller. If you add a significant amount of solar panels, you will need a controller to manage the charging cycle.
Most solar systems are directly wired to the batteries so the "store/use" switch will be bypassed.
When plugged into shore power of any kind, I would leave the switch in the "use" position to enable charging the batteries via the built in converter. If you add solar separately, it will also be charging the batteries (although at a slower rate) during the day.
There are a few good articles about solar out there and a really good intro to RV electrical systems called "The 12V Side of Life
" that is an excellent read.