Looking good, but are you using bondo spot putty rather than bondo automotive filler? I am curious because of how red it is. The bondo should be mixed and thick and usually white ish. If you sand the edges/corners down a bit and then apply the bondo, it should get the shape you want alot easier. The fiberglass method is also very sturdy, so although there may be minor cracks, you will not be able to see them through the paint and it will last you a very long time.
Yes, I'm using the spot and glazing putty on the exterior, Automotive bondo was used for the interior to help strengthen around shoulders and torso since those will be the most "weight bearing" areas. I've used the glazing putty for various other projects through my college design courses and found it to be the best for most things, so it was the first thing I grabbed for this project.