We were trying to see if an "all electric" house was possible... In in the end, we decided it wasn't. On a website that I was frequenting, people were saying that the amount of battery we had (even though it is a large bank at 618 amp-hours of lithium) wouldn't be enough to provide the heat needed unless we were really going to rough it and also run the engine to charge the batteries with the alternator. We went camping a couple of times in early March. If we had plug in shore power - no problem, the electric heater produced plenty of heat to keep us warm and comfortable. But we tried a night at a campground with no plug in and it was about -2°C that night... it was quite cold, not unbearable but it did drain the battery down to about 30%. While we don't plan on chasing snow (we don't ski or snowboard) we knew there could be times when we might be at higher altitude and experience freezing temperatures even in summer.
All along I figured this would be something we needed to make a decision on. Our choices were to install a couple more batteries (for which we had room) or have a gas (regular gas or diesel) heater installed. The cost of the two options was similar. While adding a couple of batteries would give us some heating capacity, we would still need to recharge the batteries in order to have heat for a few days. In the end we decided to have an Espar S2D2 diesel heater installed. We could have gone with a gas unit but that meant dropping the gas tank and plumbing into the tank. There were some issues with that. 1) The gas tank would have to be dropped - not so easy especially with our grey and black tanks and drain pipes under the van. 2) The Transit doesn't have huge range based on the fuel tank capacity and mileage so I was hesitant to put even more draw on the gas. 3) The gas heater unit was physically larger than the diesel (although it does have a higher heat output - but I didn't think it was necessary given the size of the van interior.) We also had a 10L fuel tank installed inside the cabinet under the sink (the heater cubby is just under that cabinet). This amount of fuel will provide heat for days. Packing one or two 5L gas cans of kerosene would provide as much heat as we wanted.) It's also easy to buy more diesel (many gas stations) but especially more kerosene (Home Depot, Walmart, Lowes, etc. all sell it.)
More money (oh well!) and a more time to re-jig the cabinet... but we're warm and happy! It will make the van much more comfortable and trips enjoyable.
Calvin here - after spending almost 33 years in education as a high school teacher, elementary teacher, and elementary administrator, it was time to retire! I did so happily and with no regrets; it was a terrific and fulfilling career. I do enjoy building projects as the design and building process is very therapeutic and you see a completed functional product in the end. Now to combine the build with another of Angela's and my passions - travel - is something we're really looking forward to.