a couple of long and hilly cyclosportives will also give you the mental strength to do race day. The lumpier the better. Yes it will hurt and be slow, but when you turn up the outlaw ride you will know that you get smash a long and hilly ride - so a long and flat ride on race day is going to be a doddle.
Oh, and you don't have to ride through the rainy night like Seren - that's just plain daft!