If your bases are constantly being destroyed then you have ventured too far. You need to ensure your defence level is high enough to withstand the onslaught from the forgotten. There are a number of ways to protect yourself, one is not to move into an area of forgotten bases that are much higher than your defence can withstand. Another is to use a script to tell you how many forgotten waves of attack you can expect.
If you join an alliance with good levels of resonator then you can withstand forgotten attacks easier.
The forgotten bases, camps and outposts do disappear respawn but even killing the camps and outposts won't help so I don't understand the comment about 12h. The forgotten camps and outposts are generated by player presence, the bases are re-generated after a set time that is much more than 12h.