I have the same problem... Captured some Naval bases in areas that produce nothing and are useless for me for any other purpose, but still have to pay the maintenance cost, when my oil production is not that high.
Solutions:
1) as someone required elsewhere, allow to destroy structures (eventually with long time to avoid that someone caputer an area, destroy everything and then lose it again, in a sort of viking raid)
2) remove the maintance cost and raise the building cost (and time, expecially for T1)
3) allow to disable the structure exactly like any other that has a maintenace cost... like unwanted railways in S1914 this can be exploited to make movements faster (it can been avoided or at least discouraged allowing a change disable/enable or reverse only once every 24h so that you can effectively keep it disabled until you need it but then have to keep it enabled for 24h before be able to disable it again, and then wait another 24h before be able to enable it again)
