He is sitting in the Howard Airbase in the northern part of sinking country
but there is a behemoth on the base
so here is how you do it
-bring rpgs, a sniper rifle and an assault rifle
-grab a chopper
-approach the base from the north and you will see a guard tower right at the dock area
-crash land your chopper right at the tower and storm upstairs. kill the guard.
-destroy everyone and everything from that position. ignore the mortar warnings from the behemoth. watch out for soldiers and kill them as they come. shoot rockets at the behemoth and unload your sniper ammo on him
-if the base is turned into a graveyard collect ammo and stuff
-storm the big building
-walker has 4 drones. shoot them first then kill walker. unload your rifles in his face
-check for additional troops now and then
i went there lvl 30, EQ 190, MK3 weapons, extra loadout perks etc.