I did this last year and am in for this year too. The worst part last year was the wind really kicking up when I started my third lap. Hopefully the wind will not be as strong this year.
My advice for the thought of doing a lapped marathon is to do your long run on a lapped course. I'm fortunate enough to live 2 miles from the Moor so was often seen lapping my way around the course route most Friday mornings. Been on this morning for the first time this year.
Actually it's a pretty inspiring sight to be on the Moor in the darkness and seeing the sun come up. Those cows don't need an alarm clock; as soon as the sun was above the horizon they just all seem to wake at the same time.
One thing to mention though is the cows are moved off the Moor at the end of October so won't be there for race day.