Newby Dry Camping Questions

Thanks everyone for the responses its greatly appreciated. I was looking at getting 2 Group 27 batteries and running in parallel so at roughly 80amp hrs per battery paralleled doubles it to 160 but usable energy is 50% on the battery correct? So Id get 80 amp hours? From what I read my fridge takes about 20ah day...then ya got water pump,water heater,LED lights inside, furnace sometimes.. Figure with all that using avg about 40ah day?? So in theory without running generator at all id get 2 full days of everything because it be 80ah half of my dual 27 battery capacity of 160ah...im trying to calculate stuff With furnace on in colder weather and also for state run campsites that dont allow generator usage or are very vague, and up to management staff onsite if they allow or not which seems to be same policy in alot of WI state parks...so bare with me GC2 batteries would cost me another $60 or so to get instead of the group 27s...they would be Costco interstate batteries.Or i can get Duracell GC2 at Batteries plus which is easier to get for me. As far as an inverter or charger can someone clear that up for me too. An inverter i prolly dont have on my rig correct...its an add on device that takes my battery power and lets my outlets work inside on battery correct? As far as chargers for 12v group 27 or 6V GC batteries....do you guys keep the rig plugged in 24/7 to keep batteries charged....or does this fry ur battery. Should u connect a trickle charger on each of your batteries when parked instead?? Or buy a Noco Gen2 or similar? Thanks