I like the idea of 2 panels in parallel via one controller. With 2 assumptions that I'm 99% positive of - that both controllers are PWM and installed 100W panel has working voltage 17 or 20 - minor difference in working voltages won't matter for one controller. His portable 50W panel comes with a huge 21A controller, so it will be able to handle both panels.
They are close enough to use together, both being "12v" panels that are approx 17v with 20/21v open circuit. You can clamp the one controller to the battery bank while the installed one is still connected and they will add their amps.
After the batteries are mostly charged up, one controller may stop adding because its high voltage set-point might be a little less than the other's, but by then the batteries will be accepting few amps and the one controller still going can do it all anyway.
Try it out. It won't break anything. You will need an ammeter to see the "action" as it develops.
2003 Chev 2500HD Gas, 2003 Komfort 26FS 5er,
1981 Frontier 11ft Truck Camper
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