Amazon will be cheaper for fabsilI use Fabsil, it can be purchased from Halfords, Go Outdoors etc - http://www.gooutdoors.co.uk/grangers-fabsil-5l-camping-proofer-p107747
Usually lasts a season and is fairly easy to apply. I've also got some in a spray can which is handy for small things such as the outboard and hatch covers.
That's two separate problems, I use Patiomagic to get rid of the green and then Fabsil to waterproof when PM has dried.