Plastic can be as good as wood with the distinct advantage that it can't rot and is imune to insect infestation.
You need some good quality plastic sheets. Fiberglass sheets are very good, but make a lot of iritating dust when worked on. Protective clothings, dust mask and eye protection are an absolute must.
You need to place some mesh over the proposed vents to prevent insects and small animals from entering.
Electro
March 2015