I find it extremely difficult to lose a Casse campaign, or even a Sweboz campaign. You just need to be willing to sit on yer arse for quite a while and just build income structures. I'm playing Sweboz and I'm rolling in cash. I have two full stack armies easily, both full of good units and I just have an ovular domain of the territories directly surrounding the 3 you capture in the first 5 turns.

The only thing I can tell you is don't overextend your economy. You just have to be patient and willing to sit for a while, build up money, buy an income building, save some more, etc. It looks like you save up a bunch of money, buy an army and go off until your up to your arse in debt and unable to pay it off without leaving you excruciatingly vulnerable. Sitting a while lets you build up an economy so you can afford that army and a defense for your new exploits.

Or, like mentioned earlier, just pick a faction that makes a shitload of money with little coersion, like the Carthaginians.