O, I forgot, 3mm poly, 8mm HDPE, 25MM HDPE. Rebuilding my tower completely. I am going to move the roadbook down and forward, more or less to the middle of the front wheel. I hit my (head)helmet a "kak hou" on the road book in the Richtersveld on day three! Still don't really know what happened, but it could have been avoided. There is just way too little room for moving with the tower that high and over/close to the handle bars.
Ideally you want your head in the exact position the roadbook is, in attacking position. My roadbook/nav tower as it is at the moment is directly under my chin, which is totally wrong.