I'm adding one additional glass mat (AGM) battery. I'll run that and watch it. Without alot of hoopla I'm pretty sure that will get us from bedtime to morning without adversely impacting the batteries. We are also fooling around with a heater buddy which is not easy on propane however it will certainly take the chill off and is safe to use indoors.
I'm with you, adding Lithium is a can of worms I'd rather not commit to unless our needs exceed the simple act of one more battery.
FWIIW I use a progressive dynamics converter that has a wired remote which allows me to step up charger to 14.2v when I fire up the itty bitty Honda generator for a top up. This setup works just fine. If batteries are low it takes a few hrs. to top up. I've got 160W of solar on the roof...it's basically a trickle charger eg nothing that amounts to much...but it's a REALLY nice trickle charger? Kidding/Not the solar will run the fridge if you do not run anything else forever as long as you have sunny days. That's alot of "ifs" ;)
*This is a good cat to deal with if you need/want a different converter:
https://www.bestconverter.com/