Yeah, mine is painted and the chassis and body are together already. The rear bumper isn't that grand a fit either, but at least it works. All I have left is the front. That front bumper fit is just poor. I tried to glue the bumper on from the flat piece of the chassis that sticks out, but that didn't have enough contact. I tried to glue it from the corners of the bumpers, but they don't sit well on the body. I finally got it to stay(for now), but it's very tenious. Now I can attach mirrors, roof rack, and running boards.
Since you haven't built yours yet, maybe you can hit this problem off better then I did. I knew even before painting from mocking it up, that it was going to be a poor fit, but with everything in its final place, it was worse then I thought.
Hope yours turns out good when you build it.
Matt