I did it around level 20 with Veronica and ED-E with no problems outside the tent.
Really, it's sad how ill-prepared the Legion was to defend the fort that housed its leader from a mailman, a girl with a punching fetish, and a floating robot.
ROFL that description is just amazing, best way of describing your group I've ever heard.
On to the original topic: It's not even that hard, except the tent. Fortunately Ceasar is happy to let you slaughter his entire camp without coming out to see what all the screaming is about. Maybe he's rosining up his fiddle bow who knows.
Inside the tent, it helps to stack the deck in your favor (pun intended) with chems and try to execute a one-shot on ceasar with the biggest weapon you can find. Pew Pew is nice for it, so is an AMR, but you'll have to freehand it because VATS would leave you without the AP to get the praetorians off you. It's a must to have a decent weapon but I found him and his menagerie easier than the legate by far. All else fails you can drink a few dozen rootbeers and start dropping plasma grenades on your feet