okay so I used the Reynold Oven bags.
everything is peachy clean
I cut them and stapled them to a wood mold.
I am forcing the stress on the bags so I did a CPOP @ 170 degrees for 3 hours ( 1 hour to go) Oven then is shut down and mold is left in Oven for 24 hours
I have looked at the oven 3 times no warping of the bags at all.
So tomorrow I will see if it come out nicely.