Update Wed. 20.1.16:
Details arrived.
Check in is near to the previously often used waterworks site around which Afon Llugwy runs (can't give away too much detail on the interweb to whoever it is that CDMCC are trying to exclude) so the rally won't be too far from there. It will be at a well established holiday camp site which has a pavilion. No fires are allowed. The search commences...
If there's a pavilion then there must be on-site loos, so it should be possible to go for a pony in relative comfort.
I wonder if it might be the site at Ogwen Bank, just East of Bethesda?