I'm not convinced about a W&G du Cros connection - the W&G script is normally very different with an underscore. To my eyes it like W&C instead (though no idea who that could be).
Hi Peter, I've seen pics of later vans in RAF use with BABS (blind/beam approach beacon system) gear - serials RAF 156717, RAF 156992 and RAF 157062. Do you have the side panels? If so, does the passenger side have some vents at the front?
The first is a Karrier WO6; and the second a Morris Commercial D type.
Info on the company here:
TRAINING TERRITORIAL PERK ■ ZEL IN THE USE OF SIX -WHEEL] | 19th March 1929 | The Commercial Motor Archive
WINTER WORK FOR ARMY | 3rd December 1929 | The Commercial Motor Archive