Setting up an rv with solar

Looks pretty good... I would suggest 2x 6 volt "golf cart" batteries in series (2x series 6v @ ~200 AH = 12 volts @ 200 AH)  batteries. You can take a voltmeter and measure the voltage on each 6 volt battery. The 12 volt batteries, you have to disconnect on battery so you can check the health of each battery with a voltmeter.

Also, if flooded cell batteries, you only have 6 cells to "water". With 2x 12 volt parallel batteries, you have 12 cells to check "water" levels.

And, I am not a big fan of paralleling batteries when you can series connect a bank.

With a 12 volt battery bank, I suggest a 250 Watt inverter per 100 AH @ 12 volt battery bank... 200 AH @ 12 volts would be a 500 Watt maximum (or even a 250 Watt) AC inverter would be a nicer fit.

If you need a high wattage AC inverter, you need AGM (or other chemistry) battery bank. Flooded cell batteries are pretty good at supplying high current--But a 1,500 Watt inverter running 3,000 Watt surge is something like >300 Amps on 12 volt battery bank... Your FLA batteries could not sustain that amount of current for much time at all.

Using the load LVD (low voltage disconnect) terminals on your charge controller for local DC power---It is sort of OK, but connecting your fuse/breaker block directly to the battery bank would be better (more current). If you surge/overload the LVD outputs, you can damage the charge controller.

Keep cables between battery bank and Charge controller short and heavy (ideally less than 0.10 or 0.05 volt drop at 40 amps). And short/heavy cables from battery bank to AC inverter--Looking for a 0.50 volt maximum drop at full inverter load.

Generally, there should be a bonding strap form the negative battery bus to your RV frame.

Tools, get a hydrometer (if flooded cell) and a (highly suggested) DC Current Clamp DMM for checking system operation and debugging.

https://www.solar-electric.com/search/?q=hydrometer
https://www.amazon.com/gp/product/B019CY4FB4 (mid range "nice" AC/DC Current Clamp DMM)

For a single 300 Watt solar panel, you do need a fuse (only needs series protection fuses/combiner box when you have 3 or more parallel solar panel strings).

For the other "fuses" in the system, you may want to look a circuit breakers. They are not to expensive and very handing to turn stuff off when working on it or turning off system for storage.

The AC inverter can use a (relatively expensive) high current fuse, or circuit breaker. Using a breaker gives you a handy on/off switch.

You can also use a 15 amp breaker for the solar array connection--Mostly because it is nice to turn off your panel before working on the charge controller (depends on how susceptible you are to sparks when working on electrical systems--Or you can throw a blanket over the panel when disconnecting).

-Bill