https://www.google.ca/search?q=Creekside+20fq&tbm=isch&source=univ&sa=X&ved=2ahUKEwib8Nq73pLoAhXWFzQIHYsCAYcQ7Al6BAgFECI&biw=1024&bih=422&dpr=1.25You have a front compartment close to the battery bank on the tongue (assumed location) so you can just put your new converter in there and leave the WFCO and all that wiring work alone.
Getting wires from the front compartment to the batteries in a TT like that seems to be usually done by drilling a hole in the floor and going under and up instead of through the front cap.
Now is your chance to add an inverter to go with the converter. Your four 6s can run a 2000w inverter which can run the MW, eg. They can share the same wires going to the battery bank. You run your shore cable into that front compartment to plug it into the inverter (via 30/15 adapter) and unplug the new converter and disconnect the 120v from the WFCO too. Fridge on LP not on Auto.
You can put a "cable hatch" in the compartment door so you can close and lock the door with the shore cable still in there for when you are away from the rig.
The rig's 12v still uses the same long wires back to the DC fuse panel as now, no need to change any of that.
Choice of converters is mostly about your own style for automatic vs manual being there, as noted above. Your four 6s can take big amps for faster charging but you need a big enough generator for that. EG a typical "2200" can just manage a 75 amp non-PF corrected charger, but a "2000" would be for a 60 amper.
(See my profile for what my choices are for inverter and converters.)
Inverters have a remote on/off switch with a long telephone-like wire you would run back into the TT from that front compartment.
That would be one way to do an upgrade. YMMV of course.
I will try to find a photo of the cable hatch in the door trick I did with the 5er we had.
