The boiler room has a total of three guards, two in the room with the prisoner and one in the other. While inside the base, be careful of the security cameras as well. The stairs leading to the boiler room should be up ahead just make sure to properly knock out the guards along the way. Head inside the red gate and knock out the guards. If you want to get the rocket launcher from the other soldier, you can lure him towards the bodies and tranq him as well. Unload your silent pistol and tranq them.
You can lob a grenade away from your location to get their attention then quickly move (don't run) towards the sandbags beside the AA emplacement. Make your way to the northwest entrance of the administration building where it is guarded by a couple of soldiers and a patrolling soldier with a rocket launcher. There's a P.O.W inside the boiler room of the administration building that holds Chico's Tape #7 so to get it, you have to rescue him as well. Leave the immediate area as more guards will converge to investigate it. Quickly go to a safe distance before detonating it. You can place the charge beside the emplacement or crawl under it and plant the C-4 there. Approach the nearest AA emplacement in your location and place a C-4 charge on it.
The enemies will also be on full alert after spotting the incoming assault teams. For this mission, you only have to destroy at leas three AA emplacements. Destroy the anti-air emplacements to make way for the operation then escape the mission area by chopper. Military heliborne assault is to the base.