As Jennifern, I'd recommend the Aquaroll auto-fill type system (ball valve etc).
The kits that connect direct to the van have a pressure reducer in them to ensure the pressure is adequate for van use, however if you ever have an internal pipe come off, then water will flow into your van, causing flooding; I know as I witnessed this twice last year.
The Aquaroll system tops up the water and draws into van on demand from the taps, so considerably less risk to flooding.
The Aquaroll brand is a daft price; I bought mine from this guy on FleaBay and it works a treat.
Of course, the option is just to manually fill the barrel; you don't have to use auto-fill just because of being on a serviced pitch.