• Two battery busses, each with both an XT60M and PowerPole connection. Each bus is intended for only one battery, though.
• One XT60M connector for a solar panel connected to a charger, which can be connected to either battery bus or disconnected. The solar charger has a USB-A output as well. A relay (internal, not visible in this model) protects the solar charger from being connected to the solar panel unless it is connected to one of the battery busses.
• Two device buses, each with three fuses protecting five device power ports, for a total of eight XT60F and two PowerPole connections.
• One 65W USB-C PD converter with a USB-A socket that can charge a laptop.
• Each device bus and the USB-C converter can be independently switched between the two battery busses or disconnected entirely.
• Not part of this box, but the solar panel also has USB-A and USB-C power supplies built in.

The design was exploratory and is not the cleanest or more parsimonious or highest-performing modeling, but such as it is, it is available at https://gitlab.com/mcdanlj/SolarPowerBox

I can't imagine anyone else wants to make this, and the planned schematic is not drawn let alone shared, but some of the parts might be useful. I did make them in a dev build of FreeCAD, so they are untested in the stable 1.0.1 release.