There are three main gurrilla camps.
1: MONTERO FARM
MADRUGADA near COSTA DEL MAR
Unlocked after completing MEET THE MONTEROS
2: PATRIOTAS PEAK
EL ESTE near SIERRA PERDIDA
Unlocked after completing MEET THE LEGENDS
3: CAMP MAXIMAS
VALLE DE ORO near BALACERAS
Unlocked after completing MEET MAXIMAS MATANZAS
Then talk to the foreman then put any facility you want but make sure you have the materials