Not sure what you mean by 'low voltage.' If you are talking about your 12v systems, You have two, a house system and a chassis system, each with their own separate battery banks. The house system powers all the living quarter 12 v needs, thermostat, (controlling 120 v Air Conditioning and LP furnace) refrigerator, interior lights, water pump, etc. The chassis system runs all the driving functions, exterior lights, dash air conditioner/heater fan, wipers, etc. The generator or shore cord charges the batteries through your converter/charger or when engine is running, your alternator. According to how your RV is wired, you might charge both battery banks when charging with converter/charger or just house batteries. Alternator also may charge both battery systems, perhaps only chassis batteries. You can test with a multimeter. Voltage will go up when charging, so you can measure voltage at both battery banks when unplugged, running engine, generator, or plugged in to shore power.
No protection is needed to 'low voltage' systems, the batteries, converter/charger will keep things correct with proper maintenance.
You mention a 'surge Guard' you might look it up and see exactly what your model protects. Some only protect against lightning or power line surges, other protect against voltage outside of 104-132 v range, delayed restart after power loss, detect and prevent mis-wired pedestals from damaging RV, etc. EMS-HW50C
By the way, your RV is wired for 120 v, not 240v. If you have 50 amp service, 240 v is available if you connect the 2 hot wires together, but normally you would have two 120 v circuits of 50 amps to use. A 30 amp RV is 30 amps of 120 v service.