Mike, 24v panels often make better use of MPPT type controllers and CAN be wired in parallel to help reduce the impact of series panel shadowing (affecting both panels)...12v panels can work with MPPT as well and can be wired in parallel or in series (to produce 24+ v, and to allow smaller wires).
MPPT controllers are a bit more costly, but can often compress battery recovery times by converting any surplus voltage (sky permitting) into higher charging amps.
Note that 12v panels are not really 12v but actually closer to 18v, thus '12v' simply refers to a batteries nominal voltage rating, not actual panel output which must be higher (due to voltage loss via wire runs and at controller) to be able to charge batts.
As far as inverter output wiring to 110v plugs goes, there are both simple and more complex ways to achieve this with differing results. For a 300w inverter the simplest way (with a factory look) might be to simply install a new 110v plug dedicated for inverter use only.
Wiring the inverter output directly into the main panel can have its share of advantages and pitfalls as follows:
1) 300w will not run most RV appliances, and doubtful it will run most coffee pots as well. 300w will likely run many TV's and computers (light electronics).
2) Wiring directly into the main 110v panel (for the factory look) can cause mishaps like, the refer switching from LPG to AC, the converter charger attempting to charge the batts (a round-robin affair), and the Air Cond, MW oven and/or water heater circuits remaining active.
3) And the possibility of a hazard when plugging into shore power IF you forget to first shut down the inverter.
Any or all of these pitfalls can be overcome by segregating planned inverter operated circuits from others by use of a sub-panel (for inverter), and a transfer switch (either manual or passive automatic) to avoid shore power conflicts. An electrician would be a great resource with these strategies, the more complex, generally meaning the larger and more capable the inverter...
Another thing to consider is that whatever wattage inverter you choose, make sure that the inverter to battery cables are properly spec'd for length (i.e. round trip length) and AWG size per your planned inverter load else your inverter will not perform properly (think, bottlenecks).
Hope this helps,
3 tons
