Nylon is a much better material for anything structural, just remember when tapping into it to use the coarsest thread you can.

If you can get hold of UHMWPE - some chopping boards are made from it, else order from somewhere like directplasticsonline.co.uk - it's extremely tough (and somewhat flexible) and light, and a good thick section of it would do great as armour.

Chuck a dirty great steel wedge on the front and you're set