Since those are small rim sizes, see if you can get Carlisle branded tires.
Your 12V battery with proper 12V energy conservation should last 3-4 days.
Replace all lights that you use with LED.
Your fridge on propane will run for weeks.
If you camp in moderately cool night time temps, your propane will last a relatively long time. All depends on the furnace cycle time. 12V battery powers the furnace fan, so again, it all depends on how much the furnace cycles on for how long the battery will last.
I installed a Thornwave Labs Bluetooth battery monitor and it has been extremely useful for gauging battery usage with different devices (fan, furnace, lights, CPAP, etc.).
2016 Coachmen Viking Legend 12RB A-Frame
2015 Jeep Grand Cherokee Summit w/Tow package