Hot glue to the top of your medpack. Using a dremel, sand the thicker pieces of foam, and cut some details into it. Then, hot glue to the side of the medpack. You can use hotglue (like I did) or puff paint to add more details. You can also use a pen to press some details in.
In hindsight, this probably would have been easier to paint if I had painted everything first, then attached. Oh well. Paint! I used a base of black, then used a gun metal grey with a bit of the purple I used for the armor mixed in.
This will attach to the shoulder of your chest armor using a rare earth magnet. These magnets are no joke, but a regular magnet will not work! They're a bit pricey, but necessary. Trust me.
To attach your plasma cannon, you are going to trace out where you want it to be, and cut that out using an exacto knife.
Using the cut piece as a template, cut out 4 rectangles from EVA foam. These are going to stack up inside your pack to give it stability.
Cut two dowel rods the height of your four EVA foam pieces stack atop each other. Half the dowel will go into the EVA, the other half into the base of your cannon. Now, you can either drill these holes, or just use the glue gun to melt them. I used the glue gun.
Install the dowel into two layers of EVA, gluing it all together.
Do the same with the base of the plasma cannon, creating a unit such as this:
Put aside. Then, put glue on one of the other EVA rectangles, and carefully slide it inside your medpack and glue to the bottom. Repeat with the next one.
Now, glue your cannon in place. Be careful! I accidentally glued mine in backwards first go around. Thankfully, I caught it before the glue dried completely.
Now, glue one of your rare earth magnets to the underside of the medpack. You will need to make sure your mark out where it should be. I put on my chest armor and balanced the medpack on my shoulder, marking in chalk where the magnets should go. Make sure you are gluing the correct side! Be very careful and take your time.
Once glued, glue a piece of foam on top of it. This should help the magnet stay put. First time around, I didn't do this and the magnet pulled right off!
Now, if you don't want your cannon to be wobbly, you're going to need an additional magnet near the bottom of the pack. I put the armor on my mannequin and marked where my magnet would need to be on both. Glue on and cover with foam.
And there you have it! Completed medpack!
If you have any questions, comments, or concerns, let me know! Until then, keep cosplaying!