protecting yagi with PVC or other material

I am in the process of building a homemade yagi (for 2.4GHz). Once done I would like to be able to protect it from the elements and thought I could place it inside a PVC pipe. I cannot find any definitive answers on the web regarding the effects of PVC and 2.4GHz. Would PVC have any effect on the RF? Additionally, is there a material that would 'help' the directionality (narrow it) and/or the gain of the yagi?



Thanks