Morden,
You have two house batteries so are well covered for lights, TV and furnace use overnight. It might help if you said what Class B you have as I suspect if it is only a year old it may already have LED lighting and all these suggestions may not be necessary. Regardless, if you don't have LED lights, with two house batteries, changing them out would only be a slight bonus. We still have halogen ceiling lights.
Just practice conservative use. Don't leave lights on unnecessarily. For sleeping you don't have to run a furnace all night long or you can lower the temperature setting to as low as you can tolerate with the sleeping blankets you have. We use sleeping bags rated down to 20F so never turn our furnace on until just before climbing out of bed in the morning. You only need to turn on your hot water about 20 minutes before using it. Don't leave it on constantly. One thing you didn't mention was your refrigerator. If it is a three-way then simply run it on propane.
With our current 2011 Great West Van Legend we have two house batteries and a generator, but over 4 years and 65,000 miles we have but 14 hours on it. We have dry camped up to 5 straight days several times. Our generator use has never been to charge our batteries. It has been mostly for testing and exercising before trips and to brew coffee in the morning. Unfortunately, unless you have a large inverter you will not be brewing coffee by running your engine. Since you mentioned truck stop, that implies to me you will be driving that day you stop and when you get up in the morning. Driving will more than charge your batteries.
I guess what I am saying is, bottom line, you should never have to idle your engine to charge batteries while stopped. You will learn that with experience.
Davydd
2021 Advanced RV 144 WB 2500 Class B
2015 Advanced RV Ocean One Class B