With two 230 AH batteries tied together in series, you essentially have one 12 volt battery, and your amps stay the same. That means you have 115 amps to work with before your batteries are drawn down to the 50% mark. FWIW, I never draw mine down that far, but as long you recharge them relatively soon, 6 volt deep cycle batteries are capable of remaining healthy.
As you probably already know, your furnace is one of your higher consumers of propane and electricity when it's running. It probably draws about 10 amps every hour it runs. Most RVers don't camp in climates that are so cold that their furnaces run continuously, but in the Colorado mountains in the winter, you're going to be running it a lot. If it runs six hours in a 24 hour period, it's consuming basically half of your usable battery capacity by itself. You'll obviously be running other things too, but only you know what they are.
I don't know where in Colorado you'll be, but consider this - in Grand Junction, there's an average of 9 sunny days each January, and there's a little more than 5 hours of useful charging time each day, due to the sun's angle (That's better than I would have guessed.) A 100 watt Renogy panel produces 5.29 amps per hour under ideal test conditions, but solar charging conditions in the winter in Colorado will never be ideal. I think the best you'll see is 4 amps per hour (per panel) on a sunny day - probably less - and that's if the panels are tilted toward the sun.
On a clear sunny day in Grand Junction, if two 100 watt panels generated a total of 40 amps in that 5 hour charging window, that's about 2/3 of the power the furnace consumes running 6 hours a day. You might want to consider getting a catalytic propane heater. They don't produce the same amount of heat an RV furnace produces, but they really take the bite out of the cold air, which reduces the amount of time the furnace has to run. And catalytic heaters only sip propane compared to LP furnaces, they consume no battery power at all and they're indoor-safe (just leave a vent cracked).
Kev