Mess provision has various protocols to be observed, but that is where Personnel might live; divided between the various ranks it is where they socialise and formal events are held.
So essentially it revolves around DUTY and is not an alternative for civvies, to the Premier Inn or a pint at the local. in my experience the latter, at most stations, is met by a coffee bar which also offers meals and a bar service.
Logically the RAFAC is not entitled, unless they have RAFAC business or are invited onto the Station by someone who is attached to the Station. Non service personnel can only access the Station by the issue of a permit granted by the relevant Station Commander.
No other person has authority to allow Station access; as the responsible person, the Station Commander is entitled to know who is on his Station.
It seems to me that holders of a MOD90 have limited entitlement – they are no longer covered by the Armed Forces Act, and if they are not on duty, they would need a valid reason to be on Station - you would not expect to gain access to Waddington or Marham where security is essential. Not being signatories to the Official Secrets Acts, it would be a nonsense.
( a reason behind the decision to transfer of Waddington ‘Air Show’ to Scampton)
Perhaps a way to determine being on duty is whether the tax payer would be expected to contribute towards any travel expenses.
And even if they have empty rooms they still would not have to let you in.
Messes fall within the jurisdiction of the relevant Station Commander who is not under the control of AOC 22 Group, so RAFAC needs to abide by the book of rules which govern them. Thus if eligible to use the facilities you will pay according to those rules either entitled or non entitled.
It also seems you cannot expect to have to Mess access as defined by rank as RAFAC Personnel are of equal status to service Rank, although there are certain senior RAFAC personnel who think they are. Also the recent review of the rules states that personnel should not be expected to share a room - something else which has escaped certain senior RAFAC individuals - I am mindful of the various courses which the RAFAC offers to ensure volunteers are trained to the highest standards…
The Messes each have a Mess Committee, with a PMC and this manages funds according to Charity Law.
Appropriate then to mention for your wider interest, that it appears the Charity Commission has an on-going public inquiry into the RAF Mess Funds and once it concludes it could have significant impact, especially when there are issues which the RAFAC manages to replicate through a significant disregard for Charity Law.
I am sure that wont detract from anyone enjoying a quiet night in the Mess, (assuming you are entitled), even though you wont have Lenny looking after your interests.