The pre-installed wiring could also handle more than 200Watts of power. If you assume the 20 amp limit as mentioned before that would be around 300 watts using 12v nominal panels 17-18 volt panels. If you use high voltage panels and a MPPT controller the sky is the limit really. Theoretically you can have 20 amps and 150 volts coming from your roof for a total of 3000 watts and not exceed 20 amps. You would have to upgrade the wiring between the controller and the batteries but that is a short run hopefully.
A single 36 cell panel (260 watts) will only output around 8-9 amps. Pair that with an MPPT controller and you would have a pretty capable system. Add another panel and you would have lots of power and still be under 20 amps.
Or you can use the smaller 12 volt panels and wire them in series for higher voltage from the roof.
Hope that makes sense.
2014 Jayco Swift 281BHS
2015 F250 XLT 4x4 Crew Cab, Short box, 6.2 gas
Solar powered! The trailer not the truck!