As we don't cover both airfields ourselves (yet!), for this one instance I'll tell you where to find information on Yeovilton http://www.thunder-and-lightnings.co.uk ... ilton.html" onclick="window.open(this.href);return false;
Not sure where to find online ready-to-go information on Culdrose though. But comparing the photo's on airliners.net with the aerial images on Google Maps or Multimap with some common sense should do the trick.
I had a basevisit at Culdrose a couple of years ago. I don't remember exactly where I wrote to, but probably some sort of PRO office. Maybe I was just lucky, but one letter was enough for a great visit. I could team up with a group of British spotters (my wife, in the mean time, actually went on a touristic tour of the area with one of their misses) and it was really a 'no limits' visit; every hangar was explored and all the wrecks and relics were checked out as well. There are many of those as the SFDO (School of Flight Deck Operations IIRC) is on base.
After the Culdrose visit, we went to nearby Predannack to see the wrecks and relics dumped there. In total, we finished with exactly 100 serials in our notebooks, a number which you could never reach from the outside.
At some time there used to be regular base tours as well for which you could buy tickets but I don't know if they still exist. For sure these weren't nearly as good as the one I joined.
My advice: do some Googling to find out about a Public Relations adress at Culdrose and drop them an email or letter!