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 Hi @ReenieG,

I wired mine so the converter was on a dedicated breaker like you want to do.  You have 5 branches in the WFCO and are only using 4 from your picture.  Correct?  Does not look like you have a microwave.

Main
#1 GFI/Converter (move converter over to #5)
#2 Alde
#3AC
#4Fridge
#5 Not used.  

Technically speaking, you would need a minimum wire size of 12 AWG to use a 20A breaker.  The wire to my converter, and I assume yours is the same, is 14 AWG.  14 AWG wire is normally protected by a no larger than 15A breaker.
Of course, the 20A breaker will "electrically" work on the 14 AWG wire; and many people have wired electric circuits in this manner.  However, doing so can increase the risk of an electrical fire in a circuit overload condition. 

This is the breaker that I installed in order to separate the converter power from the main power:  https://www.lowes.com/pd/Siemens-QT-30-amp-15-amp-1-Pole-Tandem-Circuit-Breaker/5013503419

30A for the Main, 15A for the Converter.  

This is how my Tab breaker panel was configured from the factory:


I replaced the 30A Main breaker with the new 30A/15A split breaker, for a total of 6 circuit breakers in the panel. The converter was wired to the same 15A breaker as the 120V outlets (labeled "GFI Outlets") in the camper.  I just disconnected the converter off the existing 15A breaker and wired it to the 15A side of the new split breaker.
Sorry I don't have an "after" picture.  For a mental image, left to right, of the reconfigured panel: 30A Main, 15A Converter, 15A GFI Outlets, 20A Alde System, 20A Air conditioner, 20A Microwave.   

Hi, 

From the wiring diagram, you can see the 3 wires coming from the converter.  White goes to the neutral bar that you don't need to do anything with.  Green goes to the chassis ground bar that you also do not need to do anything with.  Black or hot currently does to what looks like the circuit to the right of the main 30 amp.  That is a 15 amp breaker.  That is what on my '21 320 that was "doubled tapped" via a wire nut.  You would remove that black wire and connect it to the new breaker you install to create an "ON/OFF" breaker for the converter/charger.  When you get in, you will be able to see the wires and just need to double check it is wired per the below drawing.  The converter does not need to be on a 30 amp breaker... as it's on a 15 amp circuit (at least it looks like it).  That breaker looks like 20 amps and should work.

Hi, Yes, it looks like branch 2 breaker can be replaced with a tandem breaker to make two circuits.  Use the tandom breaker called out in the WFCO manual, THQL (or other brand equivalant).  In my 320, I did the same thing, although if I remember, circuit 5 was the tandem breaker.  If i recall correctly, the converter charger was doubled tapped into one of the breakers.  You will see that when you pull the hot wire for the charger.  20 amps is ok.  

Thanks Sharon. I've already wedged the foam insulation that came with the new unit underneath the frame piece to take care of that gap. Here's what it looks like without the trim piece. 

Nice fit ReenieG!  You may want to consider stuffing some insulation in any space between the box and the A/C unit, although, on yours, there isn’t much of a gap.