Make sure you are using one propane bottle at a time (Many years ago, my father-in-law turned on both. When he was out, HE WAS OUT !) I think automatic change over is standard now a days.
Predicting battery usage, as noted, is almost impossible. To many variables. You need a contingency plan, even if is swapping the battery into the tow vehicle and going for a 1 to 2 hour drive.
Sadly, most RV dealers will sell you a dual purpose marine battery which does NOT have as much energy storage capacity as a true deep discharge battery.
7 days boondocking. Watch your black tank level !