Leader Ironhide Cannons

I got the ROTF Voyager Ironhide cannons, cut a triangular grove out of the bottoms so they fit over the bulky arm gun holders the toy has, then filled the cut out part with a layer of sculpt.
Then I let the sculpt firm up for about 45 minutes, wet the top of it so it wouldn't stick bad, and pressed the cannons into place over the forearm bulk parts. I carefully pulled them back off immediately, waited about another hour, and pressed them on harder, leaving them on overnight.
The next day I had clip on cannons that stay on great thanks to the grooves and even peg holes in the arm bulk.
I added a little more bulk and detail to the left gun with sculpt and styrene too.