Our rig came with the GE residential refrigerator and 2000 watt magnum inverter without built in transfer switch. It has the Magnum CSW-TS20 plug in transfer switch and came with 2 small FLA batteries, a circuit of 5 inverted plugs, no solar. For the first couple of years this was fine and the GE uses very little energy so the truck’s seven pin kept the batteries at 100%. We started using the trailer more and staying at Harvest Hosts and free camp spots when on the move so I switched over to a 300ah Temgot with built in BMS and heater, and put in a 40ah dc/dc charger to charge back up in the morning when we hit the road. We really don’t boondock so I haven’t bothered with solar.
I’m no electrician and the following may not be best practice, but it may give you some ideas to pursue.
I put a 100 amp fuse on the positive battery post to the buss bar and negative battery disconnect between the battery and shunt for storage. The inverter + comes direct to the battery. After changing the converter switch to Li, I have not seen more than 52 amps going into the battery so I eliminated the original 50 amp auto resetting CB in the battery bay and now have that line fused at 60 amps. Fwiw, the 12v on/off switch (red key) in the wet bay is rated at 50 amps so I’m close there.

The atc/ato fuse block supplies power to the tpms booster, a light that I installed in the battery bay and the signal wires for the dc/dc charger. The dc/dc charger is supplied with 2awg cables from the truck using a 200 amp relay switched with one of the upfitter switches. The CB at the truck battery is 60 amps and I connect truck to trailer with an Anderson connector. The output cables from the charger are 4awg and fused at 50 amps. I have seen 39.8 amps going into the battery from the 40 amp charger.
This set up suits our needs well.
In the pictures below, the neg buss bar left to right is:
Dc/Dc charger output ground, magnum inverter ground, chassis ground and neg to battery through the shunt and disconnect switch.
Magnum inverter positive hooks direct from battery through the magnum fuse.
Positive buss bar left to right is:
Dc/Dc charger output +
#10 to original 30 amp self resetting CB
1/0 from battery +
#4 from battery to house and back from converter/charger
#10 to original Jaboni solar prep (not used)
#4 down to 80 amp hyd. pump CB and #4 up to ato/atc fuse block
Hope this helps.