I say give each player a fixed Strategic movement that can be bombed.
Units that moved are not eligible for SR
each nation can SR units equal to its total IPC divided by 10 rounded up
This value can be bombed by SBR ( he must declare this)
Example: Germany has 37 UPC and can SR 4 units or 4 points and this is the limit of what can be bombed.
SR must be contiguous line of controlled territories, except for each transport you have in one sea zone between two land territories can SR at double cost.
Example: Italy has 2 SR points and can send ONE land unit to Lybia if it has one transport. This takes up 2 SR points since its over water.
Example: UK has 46, which is 5 SR points and owns france and has two transports in the channel to allow 2 units to make it, the last point would have to be by land.