Fence Post Foundation

After reading about the hazards of mounting fence posts in soil or in concrete, I found a blog post that recommends pvc or polymer sleeves on gravel and held in place with concrete on all sides. Then add gravel to the sleeve to level the top of your post, drop in the post and screw the it to the sides of the sleeve, then fill in around the sleeve with gravel and earth.
It sounds good to me, allowing moisture to drain from the wood. Has anyone had experience with this technique? Anyone know where to get the sleeves?