Custom Mandalorian Custom Mando Helmet Bondo

This is going to be my first helmet, and I am going to use the rubies two piece jango, as I am on a budget. I am planning on using bondo to seal the two pieces together and hide the crack where they come together. This will be my first time using bondo, and I was wondering if I should just put it along the join, or if I should put it all over the dome.

http://www.thedentedhelmet.com/f23/jango-2-piece-injection-helmet-conversion-boba-esb-38437/
the picture in post number 4 shows the area pretty well..

hope this helps