Another good read is http://www.caltriplecrown.com/training.htm

The weather the past two years has been hot ... hot hot hot ... I would train for riding in heat, which means hydration, intaking as much electrolyte as your body can handle, but I think more of it is conditioning in massive heat.

It used to be a lot easier double, but since they added Cobb Mountain, it made it a bit tougher.