Thanks David, The HDPE doesn't just screw together. The more structural elements such as the base plate are attached to the chassis using bolts that go into threaded box section aluminium bar. The armour panels screw into frame underneath them to give them a bit more strength and support. The only place one panel screws into another is on the top of the oil tank where the armour piece is nice and thick to try and stop axes and is therefore suitable (I hope) for attaching straight into. I had never used HDPE before now, but so far have found it really easy to work with using just basic tools.