I'd also advise looking at the number of threads on leisure electrics. Depending on what you want to use the van for this can make or break your enjoyment of the van yet it's an area that most folks will not ask about or check (at least on the first camper!) but is an area that it's easy to cut corners on and the compromises only become apparent a season or two later.
There's places where basic electrics work, but those are mostly for day vans and short weekend summer breaks.
On a conversion done now on a modern base van there is little reason not to fit a DC-DC charger and lithium system yet many still are to save a few hundred pounds and end up with basic limited all in one systems using split charge relays and AGM batteries.
There is some argument that if it's the factory fitted basic split charge relay and AGM that's not so bad, as it hasn't cost the converter any time or effort, so long as that is reflected in the final price.
Don't be distracted by fancy control panels, ensure that the basic electrics are sound, make sure you know what type it is, that you've seen the install and it doesn't take removing half the van to get to, and the equipment is from a well regarded supplier and not, as some times happens, an unbranded maintenance charger or similar that will quickly age the leisure battery but not so quickly it would be a warranty issue.