I didn't do more than 8hrs at a time this spring but I did do something like 11 or 12 weekends were I ran Saturday and Sunday, building up to 8hr Saturday and 6hr Sunday. I was shocked how fit this made me

I'm also a big believer in a 'boot camp' week prior to tapering. 80miles/30,00ft over 10days or so and feeling great at the end gave me a massive confidence boost