The Bogart 30 amper can run 460w of panels aimed at a high sun for 29 amps plus it is able to clip the amps at 30 if you ever get more amps.
You do understand that the PWM controller must be on a 12v array with 12v batteries. (still not clear you got that) So it has to go with the 12s on the Airstream.
Meanwhile, you said in the OP you also have a 20 amp MPPT controller. A 335w panel should get around 21 or so amps aimed at a high sun, and all MPPTs limit themselves to their rated amps (or output watts, whatever,) --so no harm in using the 20 amp MPPT you already have with one of those 24v panels.
You won't be getting the full 21 or so amps very long during the day even if aimed, so you are just doing the recommended over -panelling with MPPT to get more AH haul when the sun is lower am and pm.
So you don't need to buy anything. You already have it, so just use it and enjoy! :)
