The test was for a special situation being discussed in another thread where the RV did not have a battery, but you could get 120v to it from an inverter nearby (in your truck bed or in a special box of tricks like a modified cargo trailer) powered by a battery bank that was itself being helped along with some solar or gen charger.
The question was why not just use the RV's converter to make the 12v and what would that cost you in amps from the batts supplying the inverter?
As a correction to the OP, you do need some extra voltage for the converter above 11.5v to allow for "voltage sag" when the converter is under a load.
In a previous test of my 7355 converter when on shore power, I measured these sags:
No load- 13.74
All lights on- 13.48v
All lights all fans- 13.42
Add furnace fan - 13.34
So whatever converter type gizmo is used to go 120 to 12v in the RV in this scenario, it has to be able to hold up the "12v" under typical RV loads
