not a bad idea redrun, instead of the build barrier being at the depot, have it at the fence that many can trick jump over from the inside. So if axis exit the rear they go directly into the fuel depot and then have the ability to either jump up over the wall or use a ladder to get to the roof. This would only add to the defendability, But I agree that once the allies have planted and both barriers are up, the map is over. As for dropping the defendability of the fuel dump base itself, that would require extensive brush work to change the layout of the outer wall. Maybe a simple change of not allowing mines at the blown open section of the wall near where the tank stops.
Right now as it is, 2 engies can lock down those entrances quite well with mines.