First, Hi Howard!
Second, there is a very informative thread in another composite forum. Double bag is only for process stability and nothing more. The reason for double bagging is to creat during and after infusion a pressure gradient towads the chamber between bag one and two. That way it is made sure that no air goes into the infused part. If there is a leak in bag one as soon as the resin gets there in infusion the resin goes inte the space/vacuum between the two bags instead of air in the infused part.