after you have your torso made and the jetpack, i would resin, rondo, sand, and paint both and after that i would get some straps, make a hole in the straps and then just drill the straps into the jetpack and the torso, and have other straps to tighten it is you need to. hope this helped you =D
btw the jetpack and the torso are both looking great, keep up the fantastic work =D