OK, I went around through a lot of the game... after I was given the token to freely pass and talk to Caeser,.. well, I was doing a task for the NCR and got ambushed by some Legion enemies, had to kill them... and instantly became vilified. I shot my way through Cottenwood and took the barge up to the Fort, shot my way through most of that, but get gibbed by a dozen enemies upon entering the highest tier in the Fortress.

Can I even complete this now?

Yes.

Not very re-encouraging... any hint?

Go do side-quests until you're tough enough to fight them, or simply save and re-load. Hint: if you leave the upper level, they won't chase you, so if you stick near the door you can leave to heal/reload.

Oh, and do use VATS.

Thanks for the tip. Not really set up for brute force, but meh.

i found it handy to use a granade launcher the second i entered the tent out of vats , it cripeled nearly everyone then just left came back in ect