https://photos.app.goo.gl/MvDY5pAPB3U117e56Update: Solar install and battery upgrade is complete. To answer my own original question (for the benefit of others) the stock Arctic Fox 865 battery box will hold two Sun Fun Kits 300 ah lithium batteries if you remove the oem slider battery tray. I only installed one as its plenty for our power needs.
I decided to start from just about scratch and remove the existing sliding battery tray and the battery box (with help from a Sawzall). Then installed 580 watts of Zamp Obsidian solar on the roof and routed it to a Victron 100/50 mppt controller. Then connected the oem Zamp 45 watt panel and a bumper plug in for my portable 90 watt zamp panel, to a Victron 75/15 mppt controller. Then installed 2 Victron Orion 30a dc-dc chargers in parallel and wired them to a 100amp phillips lift gate plug at the right front of the camper. Then installed a Victron links distributor and multiplus 2000/80 inverter charger. All this is tied together with a Victron Cerbo GX and routed to a Touch 50 digital display. The multiplus is also connected with a digital multiswitch for easy access to ac power. Then I tied in a generator auto start relay to the cerbo gx and set it such that if the battery state of charge drops below 40% the generator will start and charge the battery using the Multiplus. Once it gets to 70% SOC the generator will automatically shut down.
Overall quite pleased with the outcome. Will load a few pics.
