Ok, lesson #1 the hard way. Apparently when they rated Stretchlon 200 for 250F they really meant it. I had the joint in the oven with the pump running steady at 25mm Hg. The temperature was ramping up slowly and everything looked good. I noticed the pump speed change right around 240F, glanced over and saw the needle falling on the vacuum gauge. I opened the oven door and head a hissing sound. Doh! The bag had failed where it was most highly stretched in the joint fillet areas. I left the joint in place to fully cure.