question

With roof and ground arrays in parallel, you might see a conflict in partial shading situations. A higher voltage could eclipse the array that has good sun. If array voltages are similar, you will probably be OK. But you may consider two breakers, one for each array so you can shut down the one you aren't using.

Another configuration is with all panels in series. You need to insure the MPPT's maximum input voltage isn't exceeded even at the coldest temperatures to avoid damage. You'd also need a way to bypass the ground array when not using it, e.g., a switch.

Just look in the Servicebox behind the panel. There u will find some diodes. Buy 2 of these (on eBay or so) and then make a parallel connection as u planed.

When one array is in sun and the other is in shadow side, the one in the sun doesn't heat the one in the shadow an all things are good. Make some switches or breakers if u want to disconnect the one or the other.

I bought a second Victron MPPT the 15 amp one - they aren't very expensive. I wired in a switch to connect the extra panels to my yeti box (which has its own controller) for charging or switch back to the Victron MPPT. These are smaller panels than the ones on the roof so I didn't want to wire in series or parallel with my main panels. If you mix panel sizes you'll just have problems - you'll either limit voltage or limit current.

KISS (keep it simple, stupid)

2 pares of cables connected in parallel on your MPPT controller, the one pare running to your roof panels, the other pare running to a connector placed somewhere on your van where you can connect the portable panel when parked.

Put a switch or even a circuit breaker in-line on each of the 2 cable pares, if you use the portable then switch off the roof and vise versa.

If the roof panel and portable panel is the same voltage, then it will even work just like that, without any switches. Shading isn't a problem in parallel systems, it can however become a problem in series systems.

Remember to stay within the VOC rating of your MPPT controller and be sure the switches or circuit breakers you choose can handle the voltages and current involved.