>I like to use extra thin foundation. My problem has been that it quite often warps d/t heat while on the hive prior to being drawn out.
Which is why you don't want to put it in the frames until just before you put it in the hive.
>I am wondering if securing it at the bottom also would result in it tearing d/t expansion or any other problem.
You'll have better luck cutting the foundation a hair short at the bottom and having it loose. What happens is that it sags. When it's hitting the bottom when it sags, then it buckles.