I personally don't like the reb campaign. Or the reb playstile, that is. Empire for the win.
However, I had the same problems, it was just hopeless. I also thought the ai was a bit cheap here. Well, beeing cheap is something the campaign makes very easy for you.
In the first few missions, at some point just capture everything you can besides the mission critical planet. Build up your forces and defenses. Put gamespeed on fast and go grab something to drink, go read a bit, call your girlfriend, whatever. Come back and see big $$$. Accomplish mission goal. Defeat all empire space forces with your new pimped up forces, capture a few planets, get a few mines. Blockade what you don't capture (a single y or x will do here). Again Imp is a sitting duck. Mess around a bit, build more, get more money.
From there on things should start looking rather too easy, if anything.
Well, I'm not saying it's the best or most heroish way of doing things... But I don't feel too bad about it, even though I consider this strat cheating. We are playing against an AI that doesn't feel to bad about cheating it's a$$ off, too...