At the risk of teaching you all how to suck eggs...
The name of RAF fields comes from the postal address of the Officers Mess. You can see this particularly well in East Anglia.
Right, St Asaph. It's another generalisation again. The airstrip was at a big country house called "Dolbelydr" (the spelling was Anglicised - so no surprise you couldn't find it!) The house is now owned by the Landmark Trust (
http://www.landmarktrust.co.uk/dolbelydr.html) which has started to renovate it (it's originally a 16th Century building and it is the home of the Welsh Language (well, if you believe the website!).
Like most of these big old houses (think Woburn Abbey) there's always a spare bit of land for an aircraft.
I can't immediately find it on the map, but it's got to be on this map:
http://www.multimap.co.uk/map/browse...multimap.y=175
Hope that helps!
Dai.