This is where to put the chest texture PNG files:

    ender.png
    normal.png
    normal_left.png and normal_right.png (or normal_double.png, for resource packs from 1.14 or earlier)

from the "\assets\minecraft\textures\entity\chest" directory in a Minecraft resource pack in order to make terrainExt.png.

See mineways.html (in the docs directory, or http://mineways.com/mineways.html#tilemaker) about the TileMaker for more information.