H13, I was just pointing out that we could use the airs without the genny running and know that extra fuel would be used in that scenario when going down the road with the engine running.
As far as I know, our genny is only set up to come on if the batteries are low. I have a feature that I can set it to come on the moment there is loss of shore power. I set it for that feature when I'm in an RV park when I have the air running as not to load the batteries too heavy if shore power is lost.
I only use the electric heat, or any heat, when connected to shore power. I never use the webasto at night, only electric heat. I also never used our Aqua Hot at night in the other coach. The dash heat is amazingly hot and have needed a couple of times while driving. The cockpit has a driver's unit (air and heat) and an additional separate unit that includes the driver and passenger area for extreme temps whether hot or cold.
I just don't like fumes around the coach when I'm sleeping so anything diesel fired will not be on unless it's absolutely necessary. And you are right, the heat pumps don't work well under 40 degrees as we had that experience in TN after we picked up the new coach. We were back home for a month in TN and I ran the webasto and the electric heat during that time. We have an 83,000 btu diesel heating unit and I do notice it uses a lot more fuel than our previous Aqua-Hot.
Safe travels,
MM.