So I've been helping a few people out by answering questions about my build for their own Crusaders and I thought this particular bit might be helpful to others as well.
My "Bondo Sculpting"
Step One: After you have your base piece ready sketch out your finished design as a guide.
Step Two: "Bondo Sculpting" As you can see, you don't want to put it on all pretty like.
Step Three: Sand. Once this has been done, you can see by putting the Bondo on a little sloppy it will give you a very organic end result.
Step Four: Add a bit more Bondo if needed. It's best to build up areas gradually then try to slap it all on at once.
Step Five: Sand again. (And continue to repeat step four and five till you get your desired result.)
Step Six: Don't forget to check the side views to make sure you get the desired dimension.
Hope that helps.