Was trolling hard yesterday with the Harasser E, went out ahead of my team (who were camping hard on sandblasted as usual) made about 120k in a few minutes. Making money isn't that hard as long as you're doing damage at all opportunities.
I was shooting at sullas flying by, spraying down oros and owens, and even rambo charged a catapult (though I had to run away because a Ncat saw me). I died several times actually but still had no trouble making money.
One thing you need to keep in mind is that there exists earning modifiers. Thus taking the most expensive kickass thing you can will demand that you do more damage than if you keep with cheap shitty assets. This is because the money you receive is modified based off the asset you are attacking and the asset you are driving. Therefore if you are spraying down a Mcat B in a Harasser E, you are getting lots of money even if you're not doing too much damage. Mind you this is no official announcement but I do recall the Toth explaining such a system some time back.
Indeed, the hardest assets I've found to maintain are Assaults, because it takes so long to plod and repair and those repairs are expensive; it really demands that you do lots of damage which is hard when you're always instantly focused.