It's to do with the origins of patronyms, that some were from professions (Baker, Butcher - don't know of any Candlestickmakers), others descriptive (Douglas, White) and others topographic, where they were from. "van" is the Flemish/Dutch for "of", and either referred to a commoner from somewhere - in which case it was classically spelled with an upper case V - or was from the noble family who were Lords of the place - in which case it was a lower case v. The same applies to the Francophone areas of the borderlands, de=nobility, De=commoner.

The Dutch having pretty much done away with the feudal system a few generations back decided that to emphasise this, all Vans would become van, and so it's only in Belgium where it remains significant.

So, unless Dave can show he is descended from the Lords of Ronk, he should correctly use the upper case V, just to show he's a good ole boy.