Yep ... I have the same question: How's the above different than just setting a PD unit to boost voltage as long as you want and as often as you want using it's handy-dandy remote control? .... and the PD unit can of course be built into your RV, too, in place of any stock converter that may have come in the RV.
Using a separate power supply may be cheaper ... unless you can find a good deal on a new or used PD.
Using a separate power supply for charging an RV battery bank may be cheaper - especially if you already own one - but of course using them takes more messing around whenever you charge the RV batteries. Hit and run RV'ing is not too compatible with messing around. Permanently squatting in a spot for weeks on end with time on one's hands may be another deal, however.
I'd prefer a Parallax 7345/55 timer controlled dual voltage T unit, instead, in our RV.