That front cyclerack is sure nice when riding 2-up and needing a little more room for storage. I can't put the pack on my back as it gets in the way of my wife and she would really prefer not carrying it so the rack easily carries the pack. And, she is very comfortable on the back of the TW - ha, except when the trail looks bad so she gets off and walks in those places. Of course those short breaks like that are the secret to her enjoyment of the ride.
It has been my experience that when running low pressure off road that the main problem has been the tire slipping on the rim gradually - mostly from braking on the front tire and spinning of the rear tire. The tire finally rotates enough to rip off the valve stem. So far, this does not seem to be a problem with the TW (maybe the 6-ply or the rim bead?). I've been monitoring this by turning the nut up to the valve cap so if it slips you will notice the valve stem getting sideways and it will also have to slip quite a bit before damage is done.