This maybe an unpopular answer, but here goes.
If plugged in 24/7/365 (park model that never moves) and had my slides out permanently then why waste money on 3 stage converters and new batteries?
I say remove the batteries and tape the cable ends. The batt isn't doing much for you if always plugged in anyway.
Then get a 45-65 amp single stage converter and it will provide all the 12v you need and be cheaper as well.
Now if the unit ever moves you need a battery for slide movement in/out and the trailers emergency breakaway brakes.
A disavantage is if you leave refer on while away a power outage will spoil the contents where as having a batt installed will give some backup service to the refer. Also if the converter fails you'll have no backup source to run refer, lights, etc.
It's all just a function of the size of your wallet.