One obvious question: why CF or kevlar instead of layering them? I would think that the properties of CF and kevlar would be very complimentary to eachother in this situation.
You are right that the tank narrows rearward, and that low-side slides likely wouldn't touch the rest of the tank, but that is on tarmac eh? On the dirt, and in the rocks and such the rest of the tank is still vulnerable. Perhaps this is a small concern and not worth guarding against.
ps - why not wrap them around to bolt onto the front tank mounting hardware?