Damn Dave, it's so easily done though. I've reversed into one of those stupid green ones at Asda once but luckily it was bendy and didn't damage my car. I also did it again to a steel bollard that ran around the carpark but was below my mirror view and I just touched it, thats left a nice scratch on the side of my rear bumper but luckily nothing else. It happens to everyone, don't beat yourself up over it.
If you go through the insurance then i'd take a bammer to the back window as they replace the window you currently have in a new tailgate so i'd get the new glass also.
Let us know how you get on and I hope it's all resolved before TRAX, if not then just bring what ever you want along, maybe even your bike