I may be mistake but I think that Gannet SAR flight (The UK's busiest SAR Flight) have 2 Aircraft and 4 crews....sometimes 3 1/2 crews
Sometimes significantly less than that!
The whole plan seems to be based on historical statistics. Generally speaking, Chivenor gets a reasonable number of Med-Transfers during the night, together with a few searches, but not many immediate life saving jobs. However, they do get the rare high profile long range night rescues and major incidents.
The long range rescues will go to Culdrose when the fleet it unified and I think the major incidents will be taken on risk.