Hi
@Linc, The Victron 100/30 indicates it can handle up to 100 volts input and give up to 30 amps in output at whatever battery voltage is. I have mine (2 X 200w panels and 1 X 180w portable panels) connected in Series to a 120ah AGM battery. I have seen up to 23 plus amperes into battery when load has been high and battery voltage around 12.3 volts in good sunny conditions.
If connected in Series, you rely on VOLTAGE rather than AMPS. Also, if connected in Series, amperage is limited to the lowest output of any panel but voltage is highest. If in parallel, amperage from EACH panel is cumulative but voltage is limited to the average output of all panels. There is much less loss of current with the higher voltage when in Series and one can use thinner wiring. If in parallel, voltage losses need to be considered in connecting panels to controller, especially if distance is involved. Each panel has a open circuit voltage of around 22.5v and a "working" voltage of approx 18.0 volts, but this drops as load is applied to approx 16 to 17 volts. My panels have a "working " voltage of 18.3 to 18.5 volts when under light charging load (battery fully charged and in Float mode) hence up to 56 volts possible and low input amps to charge or carry light load. So you could connect up 4 panels in series and your MPPT controller can handle up to 100 volts.
For your setup, and with all the panels, I would consider that a 40A unit would be preferable as you did indicate that you may connect extra panels, which I guess would then have to be connected in PARALLEL. You cannot connect one set of panels in SERIES and then connect extra panels in PARALLEL to the same controller. Examples of operation to consider:-
In series, I tend to get more current from controller to battery/ies especially if light is low or changing frequently, but if one panel is shaded or partially shaded, current drops off but voltage stays high. Only 1.98A total from all three solar panels (measured with clamp meter) at 56 volts (on clamp meter and controller) still gave me over 7A output from controller into battery when battery voltage was 14.0 volts - the advantage of an efficient MPPT controller.
However, if I had the panels connected in parallel, I would need to get approx at least 2A from EACH panel or more from the ones not shaded or partially shaded and have heavier wire from my solar panels to reduce voltage losses to controller. With flat panels on roof, you are going to have to place van in sunlight for best results as max solar generation is between 10.00am and 2.00pm. Before and after that, solar generation is considerably less. Or if in shade or partial shade, voltage is more important.
@Crusty on this forum has his panels connected in Series, has great results in low light and max generation when in full sun. I believe you will get good feedback from a member with REAL experience in solar generation with a MPPT controller and fixed flat panels on roof of van. As mine are all portable and I am able to follow sun as necessary, my experiences are not necessarily the same.