@Nikita just doing the tutorial for the action cam the back detail. It could have been done by duplicating the body curve and cutting it right through the extruded blocks, then using this as a bool cuter into the main body. this way you maintain the curvature of the body for the cutter.
Superb tutorial by the way - for anyone not done it yet. If you're going to buy at least one make sure it's this one you learn so much in a short space of time.