You can find that hole outside of Airbase. People cannot see you from outside so make sure you are not making any noise. Clear the area before you all get in that hole. Repeat the operation for every team member getting in that Hole: if you are separated and do not hide at the same time, one of you can make the whole team spotted. If this is the case, you are very vulnerable to grenades so try to get out as fast as possible. Sacrifice team members if needed, remember only one of you is needed for the final victory.