This widened back (made for a scaled up Space Marine model) was done in a simpler and cleaner way to that featured in my Artscale Tutorial. The basic approach is to cleanly chop a single back pack in half down the centreline. Glue it back together with a plasticard spacer in the middle (approximately 3mm). At the top fill in with Green Stuff and score lines to into it. Then attached layered armour plates over the remaining gap. This could be done with plasticard but on the example above I sculpted one piece in Green Stuff and made a mold using Blu-Stuff. The rivets were added later (Grandt Line premade rivets).