When I was visiting my mum I noticed that the local council had replaced all the bus stops with really nice, substantial wood ones. On closer inspection I realised that they were plastic. Needing to replace the piece of timber which sits on top of our gantry and has aerials and lights etc attached I did a bit of research and found a company that supplies this plastic timber. I comes in various types and colours including white. It is used for all sorts of things on houses and in gardens and is guaranteed maintenance free for many years.
I purchased a 5 metre length of white and have been really impressed. It cuts and drills well, you just need to go a bit slowly to make sure that you don't over heat and melt it. It takes a screw just like wood and planes and sands well. It weighs about the same as timber but is not quite as stiff so I don't think I will use it for the dinghy seat which also needs replacing. (won't take my weight!!)
I will cover this on my website and see just how it works out but according to the adverts it should last for many years.