I'll chime in here. I kept my tanks running with a generator. Getting the 20g I needed a day to keep my 6500w honda running was a problem. Finding as store with gas and power at the same time required driving in the snow and ice everyday.
Getting into solar and powerwalls is cool and all but it will only buy you a limited amount of time during a power outage. Due to the cost and all the other factors this is a distant thrid option. A generator and stock pile of gas before the weather event will be your second best bet. I personally am installing a whole home generator that runs off natural gas with a propane backup in case the natural gas grid goes down. The cost to install a large generator and permanetly wire it in with an automatic transfer switch is total $ about 3 times what the generator costs. Most of the cost is in site prep and gas line prep. Almost no residential house has a propey sized gas meter and gas service line to fuel a 300ft3/hr generator. Its a very expensive option. For me it will be a have to have as the volume of water in my house would be too much for a single 6500w generator which costs 3k already. Also as stated over coming the thermal difference between 47 inside up to mid 70's with drop in heaters can almost be impossible. For record my tanks run 1k watts of heaters. The options suck but if your going to stay in the hobby long term the expenses start to add up quickly.