Op, our family dry camps 4 days at a time. Idaho, so mornings regularly in the 40's. We run the furnace an hour or so a day. I have no solar or generator. You mentioned a fridge you use that runs off batteries, mine is standard RV fridge uses propane. My point is our camping styles are similar. I researched batteries a ton, found much help on this forum. If your looking online they are expensive because of shipping a 70 lb item. So go to a real RV center (not Walmart) you should find dedicated RV batteries there. True deep cycle, golf cart type batteries readily available for around $149. Trojan has a dealer locator link on their website, use it to find one near you.
Just because Walmart and auto zone sell multipurpose starting/RV type with CCA ratings doesn't mean there still isn't a need for deep cycle type batteries. These aren't something you purchase online though.
