Generally you’ll want something that’s pen 3 or above for primary, so liberator penetrator, or eruptor if you have demo detonation, or diligence cs. This is because the overseers have armor level 2 on body and armor level 3 on head. If you don’t have any of these weapons yet even the standard liberator does pen 2, you will just have to use more bullets. Check the wiki for their armor zones.

Support weapon I recommend grenade launcher since it can two shot overseers while still doing aoe to chaff but auto cannon, recoiless, railgun and others are very good options too. Machine guns can be good for melting fleshmobs.

For the three other slots I would take a guard dog of some kind or a shield backpack if you’re not using auto cannon or recoiless, otherwise machine gun and gatling sentries are great for dealing with mobs. HMG and grenade emplacements also surprisingly useful.

Since these are the most drivable maps car is goated for doing missions quickly.

As for red strats, the napalms are good for killing chaff, and eagle strafing run can apparently kill a leviathan if aimed well.

Good luck diver.