If you only need to warm the camper up in the mornings then the Buddy Heater suggestion is a good one. That way you don not use the furnace at all.
But, if you have a lot of Phantom Loads and run the lights a lot a single battery still may not make the whole weekend.
There is a lot to learn about this sort of thing and we do not have all of the information we need.
It kinda depends on you as a individual too. If you only want to do it this one time and never plan to do it again you might try bringing along a second battery and some jumper cables in the back of your tow vehicle. Set the second battery on the ground when you get to the park and then use the jumpers to hook it up to your camper battery and it will give you more hours.
It's messy looking but, I have done it in the past. (But, I'm a Caveman and I do stuff like this )
Make sure both battery's are really fully charged before you leave home.
After awhile I decided to just get 2- 6 volt Deep Cycle golf cart batteries. I also changed all my light bulbs to LED's because they use so little power. I also shut off some of my phantom loads. Now I can do a weekend easy. Including running the furnace in the mornings.