It now appears as though Eastern have 12 bases for the operation of 24 aircraft. They are long over-due for a radical rationalisation of bases to cut crew and engineering costs, but they seem to keep on adding bases instead of working out how to operate the same routes from a reduced number of bases
Crew and engineering costs won't increase as much as you think... if at all! Opening up a new base won't have an affect on crew costs since you will need the extra crew to operate the route regardless of where they are based. Eastern don't have dedicated crew rooms at most of their bases so any extra costs that would be incurred would be small. Eastern don't have a line engineer at all their bases either and if they don't decide to base one in SOU then they will probably carry out frequent swaps with the LBA or the NCL based J41 whilst it is on the ground at SOU so that the aircraft can be rotated round the network for any engineering that will be needed. The only cost will be somewhere to store the catering supplies since the catering is done in house. The stores for the catering could be flown down from one of the other bases saving costs further! This may seem like it is a bit Mickey Mouse but that is why the airline is profitable and continues to be so. They won't have a problem finding crews for a SOU base since there will be a few flight deck that will happily move down since home or commitments are down south.