Allied rear fields (with SpitVb, HurriIIC now enabled) are airfields: 1, 2, 4, 5, 21, 22, 30, 31, 53, 54, 56 and 57.
And for the Axis the rear fields that have the 109F enabled now are: 33, 34, 35, 41, 42, 43, 50, 62, 63, 64, 65, 66, 74, 75, 76, 77 and 78.
Or at least they should be, I hope I got the numbers right.
I'll try to add that to the MOTD at some point (or perhaps one of the other staff members will?).