Battery Low Voltage protection

www.amazon.com/Blue-Sea-Systems-Voltage-Disconnect/dp/B00GZOP53M

I don't have one myself, however Blue Sea Systems is a very reputable company.

Victron is also a very reputable company:

www.amazon.com/Victron-BPR000065400-BatteryProtect-12-24V-65A/dp/B01N6ATT8C

Keep in mind that since the battery supplies the entire DC side of the RV, you want a disconnect with a high continuous amp rating.  I would not go below 30 amps.  The lower rated disconnect switches are more for light loads on the battery such as a radio, not the entire DC side of an RV.