The wiring most at risk is the wiring between the two batteries, your F2 does not protect this. Both ends of this external wiring must be protected as either/both batteries can provide current to a fault in this external wiring.
Fuses are not generally used for the PV module as it is not a source of overcurrent. Most charge controllers do not allow any backfeed to the PV module, so a fuse is not needed there. Any fuse internal to the light fixture (F2) that is part of the manufacturer's wiring must remain as manufactured.
If both batteries are not in the same thermal environment (operate at the same temperature), expect short battery life.
Your diagram shows grounding of the PV negative, this is incorrect. If you are grounding the circuitry, do it at the battery negative. If you do not ground the circuitry, then you should use 2-pole circuit breakers where needed for overcurrent protection.
If you can, see Exhibit 690.5 of the NEC 2011 National Electric Code Handbook for a general diagram. The example does not fuse the inter-battery connections because they are in the same enclosure.