1.  Display spawn arrows for your country's bases only. 
Removes the big yellow "spawn camp HERE" arrow.  Another option is to provide a general arrow showing the direction of attack from enemy bases without giving away the exact spawn location.
2.  Provide 2 or 3 spawn options per attacked base. 
Just far enough from one another to keep 1 guy from camping all.   Even if this limits the total number of bases attacked due to the launch graphic.  EX.: 1 VB has 3 spawns attacking 1 base to the north and 3 spawns attacking 1 base to the south.
3.  Blink arrows that are being camped.
This will give some notice and allow player to choose another spawn option.