Pete:
Welcome to the forum.
Thanks for the informative post... very good for a newly welcomed member!
Am in the planning stages of the 110 Dormobile Camper and while we are going to use an Airtop the need for auxiliary power is shared.
Instead of drawing power from a single battery, there are a lot of small 12V GMT Deep cycle batteries that will fit the unused space in the battery box under the left seat.
We installed several of these to run various things, but these batteries can be discharged and recharged many many more times than a standard car battery.
We used two 200 AMP relays to direct the alternator output between the two batteries as well as a relay to connect the field wire.
Then you can run off the auxiliary battery for things like the heater blower.
Sonic Electronicx has a very good selection of small GMT batteries.
https://www.sonicelectronix.com/cat_i228_car-batteries-power-cells.html
You can match up the space available for the auxiliary battery and the amount of 12V power your application requires.
There are other suppliers as well, but Sonic usually has the best pricing.
Hope this helps Wilboro.