yes Welford has its own eastbound M4 exit marked "Works Unit" but in red which is a bit of a giveaway - plus the CND mob regularly paint some abuse on the sign (which is then repainted)
From the M4 westbound you can see what looks like standard USAF type security tower but not the site - which is a monster arms dump
Whenurhappy 's suggestion is interesting - its only a short drive from Greenham Common and is a "Secure site" and those pads on the eastern side are are quite long with sweeping entry ways - just the thing for a 60 ton GLCM launcher
hmmm...................