Typically 20-30 miles a week here. I did my first trail marathon off a longest of 15, and first ultra off a longest of 21. They do get easier as you do more and like Cougie above I wouldn't necessarily recommend it as a strategy, but if you're reasonably pig headed you can normally get round.
Don't know if you found a place - give us a wave at checkpoint 2 if you did and help yourself to cake! I've done it a couple of time and reckon it's the perfect next step from the marathon. Not too far, well marked, well supported and pie at the end
Glad you enjoyed it - nice time too. Don't shout about the clips! - they were a bonus and not everyone got one! (...which inevitably prompts complaints!) They were last year's goodie and we actually gave out over 600 goodies bags to people who'd run the course anyway in foul conditions after we'd cancelled.