Thanks for all the advice.
I live on the coast and I think can get west systems products but not having used them before I am more inclined to try the spray on polyurethane Glen suggested. I don't have a spray gun but saw this aerosol can is available at Bunnings:
http://www.bunnings.com.au/british-p...thane_p1400040
It looks to be UV resistant. The tube is small (6 inch F5 scope) so two cans might be enough.
What do you think?
Thanks
Rod