A single group 24 battery is at best 80amp hours. Using an inverter to power your 2 mattress pads and you would use the formula:
ACwatts/12voltsx1.11=DC amps The 1.11 is to compensate for a 90% efficiency of the inverter which is being conservative.
2 heated mattress Pads, 180watts each (which is a number I found for some popular pads on the net) you get 360 watts per hour. Multiply that by 5 hours (an assumption that it will run for at least 5 hours in an 8 hour period) and you get a total 1530 watt hours. Divide 1530 by 12 (12volts) and you get 127.5 times 1.11 and you get 140.25 which is the amount of amps you will need to draw from your batteries. You can see that your 1 group 24 battery having at most 80 amps will be dead before morning, like I said you will be using lights, the furnace (even sparingly), water pump, lights, etc. It will not work on 1 battery
Now with 2 6volt batteries you will do a little better with around 220 amp hours but that means you will last about half way through your 2nd night out without recharging.
If you plan to run generator during the day to recharge the batteries then you can do it but you will be running the generator EVERY day. This gets old very quickly when your aim is to be out and enjoy some peace and quiet in the great outdoors camping. Not to mention if you have neighbors they won't like you much at the end of the first day.
Lots of great information about 12 volt systems and the formulas I have used here area available at:
With our old motorhome we ran 4 6volt batteries. I installed a digital programmable thermostat which ran on A-cells available from Home Depot with which I could program the furnace to automatically drop temperature at night and come on just before the morning. The furnace would typically run once during the night maybe twice depending on outside temps and the inside temp would be around 55, then we loaded up the bed with lots of blankets and a down comforter to stay warm. We were usually good for about 3 to 4 nights out this way and would occasionally have to run the generator to put a bit of charge into the batteries. Keep in mind I wasn't using an inverter to power anything at that point. Just a light here and there, water pump and the furnace.