@Captain Quick My understanding, from reading the various threads on this forum, is that the VW split charge relay system has an engine run signal feed to control the relay switching, so swapping out for the Renogy will be straightforward.
The mains operated battery charger that
@sarah_86 mentions is located behind a panel in the cupboard that houses the circuit breakers and water heater switch, just to the side of the rear seats and is rated 16A max for lead acid type batteries only.
My intention is to eventually go Lithium; so my 1st upgrade to the electrical system is going to be the mains charger, swapping in situ for a Victron unit and then replace the split charge system with a Renogy DC-DC over the next winter when the van won’t be in use. My plan (which may change) is to actually put the Renogy under the drivers seat as that only has the heater pipe under it and so there is plenty of room, giving me more space under the passenger seat for a larger Lithium battery at a later date.
I’ve currently only spent single nights off grid and book EHU pitches for longer stays; I have my doubts that the system supplied by Hillside would last a full weekend, but I’ll put it to the test some time this Season (Which is my 1st, so it’s all a learning experience).