I had a much easier time of things.
I sent one guy up to the north gate with a sniper in one hand and an fn fnal in the other.
I sent three to the west gate, one pancor at the front, two snipers at the rear.
I sent my heavy weapons guy to the south gate with his newly aquired browning m2 (you can get em from the guys on the hill to the west in St Louis)
The north is only attacked once, and is mined anyway, so it's a fairly light attack. A couple of mutants might make it to the gate, but they'll be weak as hell and easy to take out with a burst of fnal. One sniper can cover that, switching to fnal when it gets to closer combat.
The south gets a lot of mutant attention, but the one guy with the browning made short work of them, since they're mostly melee mutants which group up : the browning ate them alive. I set him to 66% aggressive and didn't even bother watching him. He didn't even get hit.
As for the west, your two snipers will make short work of most of them, and the pancor/caws guy will chew up any that dare to get close. After the first west wave, send your pancor guy around the barricades, and behind the fence outside, to find two lurking mutants. Wipe them out, and they won't cause problems afterwards. Send your pancor/caws guy back to the barricade again; the next attack will fail like the first one.
And that's that. I don't think I lost a ghoul; annoying since I had to steal the sniper rifles and ammo off them rather than looting their dead sloppy bodies. You win some, you lose some I guess.
Oh aye, you're probably wondering why I only used five characters; Two reasons. I deliberately developed a well rounded squad of five so I could fit em all in the tank (lovely vehicle, that), and that I'll get the stat bonus when I finally manage to get the pipboy encounter.