Help : Half Life Ii ?

IN the chapter sandtraps
i enter the base , there are 3 watch tower
i beat them all
then 3 post guard the base
i destroy all of them
then a gunship shows
i destroy it
after that i search for every single thing in that base
but i can't find everything
i stuck in there
what should i do?
shot the walls with the RPG?
use the gravity gun to blow the wall?
throw the bug bait?
what should i do ?
i look the walk through
it says blows something up
it so strange i blow everything in the base but nothing
and nothing happens help me plz ?