Start training NOW! There is simply no substitute for building up you anaerobic and aerobic capacity, muscle strength and stamina. I am assuming you would not have taken it on if you did not have some reasonable level of fitness to begin with it so you should be starting with four sessions a week building to five. I am not a MTB user but I’d reckon a couple of sessions could be straight roadwork (or the gym equivalent) to get those muscles, lungs and circulation working under prolonged oxygen debt. The other two should include actual track work prepare for the vagaries of the event itself.
I’d be buying a motocross kidney belt if you don’t already possess one. Great support for the lower back and stops the internal organs being bounced around as much.
Badsville, its not the falling off that hurts... it’s the coming to a halt at the end of the fall...
MatthewB, I assume the hip flask contains your favourite energy drink, be it Red Bull or whatever. The last thing you need is impaired judgment and reflexes from alcohol consumption. Even a little has its effect.
Lastly, you are a braver man than I. Good luck good sir!
Blue