OK, so I'm not getting it.
1) Are supposed to be used with more than one battery. Yes most dealers only put one deep cycle in your rig, normally due to it's an extra cost above and beyond the prep charge and "they" charge to much for them too.
2) Residential refrigerators are normally ran off inverters with voltage monitoring.
3) I have tested my Frigidaire turned off for 6 hours and freezer temps raised to 28 degrees from zero.