I had the same issue with the chassis battery in my old RV. What i did was add a marine type single bank charger under the hood and ran a plug for it from the coach itself. This way the battery charged, maintained as the marine cahrger is completely automatic, was ignition protected, was designed for a harsh environment. These chargers are designed to be permanently installed and can see the charge from the alternator with no ill effect. Worked flawlessly and allowed me to listen to my stereo all day long...
