Most people use sintra, or fiberglass to make their armor (including the jet pack). You can also use aluminum for a more accurate look and feel. Yes, you need to cut slits in the backplate to hold the jet pack. The trick here is to have some sort of harness that you wear under your flak vest that actually holds the weight of the jet pack. The strain on your backplate from the weight would make it fall off, because most people use either velcro or snaps to hold the armor on. I just got a military harness of ebay or you can build your own. A good site to go to for a decent tutorial of an inexpensive harness is tk409.com as well. Hope this helps. Cheers and good luck.