I wonder where Saudia Cargo will fly too as they have already announced that they are ceasing operating from Manston at the end of April but apparently they have said that it was the airport of choice for there customers primarily bringing in fresh produce from Kenya so maybe LGW might get this service if Saudia Cargo wish to retain their cargo flights to the south east of the UK.
Depending where the ultimate final destination is, I would put money on STN (that's if the flights are to continue, it hasn't been said they will).
Gatters doesn't seem to do much in the way of all cargo flights, and with Saudia now having a relationship with MAG (in the form of MAN flights), and STN's good cargo sheds, it would be like missing an open goal if they didn't get the flights.