Slab built piece warping during glaze fire

I've been making some holiday pieces with slabs and a bit newer to hand building. I current have some 3D Christmas trees ready to go through bisque.

I did a hand built slab menorah that I dried with support and it stayed pretty flat until after I glazed it and then it warped a little bit (white stoneware, cone 6 community kiln firing. I know they use witness cones, but have no idea on the actual firing what the cones told them).

Any tips for trying to keep future pieces from warping? The 3D Christmas trees are rolled out to 7mm.