anyone have bondo tips?

Get a 10" half round cheese grater-style body file. After you spread the filler, don't overwork it, leave it as smooth as you can and let it go. If you work it too much, it will start rolling and crumbling. When it becomes the consistency of soft cheese, use the grater to rough out the shape you want, but don't over cut and remove too much. Especially, don't wait too long and let the filler cure too hard - takes a lot more effort to work it.

Let it cure a little more until you can start smoothing out the grater marks with 40 then 80 grit sandpaper. Don't get in a hurry or the uncured filler will clog up the sandpaper. On flat panels use a longboard with your sandpaper and keep the board at an angle when sanding - work on the diagonals, not side-to-side or up-and-down.