I've been thinking about the stacks... PVC glue just wasn't working as it's not really made for contact joins. (You're supposed to slather a smaller pipe with it and fit it inside of a larger one.) I figured I could use the zip ties without taking too much away from the costume. It'd also prevent accidental breakage.
I prepped the pipe yesterday by giving it a coat of silver spraypaint. Because PVC doesn't dissolve like styrofoam, I was able to use regular spraypaint. So far as I know, Krylon doesn't make H2O Silver.
Next I drilled two small holes in the side of the larger pipe that would be facing the body and fed the zip ties through. It was easier than I thought, but only because I had the foresight to not connect the longer pipe first. (Unless you've got foot long fingers, you're never feeding the zip tie through the second hole.)
Next, I drilled three holes in each, the longer pipe and the shorter pipe, that were equal distance away from each other. These holes would house the zip ties that hold the two together. I fed the ties through and put them on loosely as I went. If I had done them up all the way, each succeeding one would've been a total pain to put in.
It looked like the stack would hold together really well, despite being a bit ugly now. I drilled two sets of holes in the shoulder (the part that would be facing away from the torso) and fed the ties through.
For added strength (read: think of a smokestack getting ripped off of thin flimsy styrofoam) I put a dowel under the zip ties. If anything caught on the stack, they'd have to rip the dowel through now as well.
Finally, I cut out an Autobot symbol I had printed up and glued it onto the arm. There had to be SOME glue in this step, heh!!!