I wasn’t sure how to set the texture coordinates - I had only come across scaling so assumed that’s what “set the texture coordinates” was in reference to. Anyway, I have figured it out, so thought I should reply with an update in order to complete the thread and help others. Please clarify anything I have got wrong?

So my box is 0.25 units tall, 1 unit wide - the texture coordinates need to reflect that. It looks like to set the texture coordinates (the “UV map”), you need to change the values set in one of the box’s buffers, like this:
[java]
Box box = new Box(/etc/);
box.setBuffer(Type.TexCoord, 2, BufferUtils.createFloatBuffer(new float[]{
1, 0, 0, 0, 0, 0.25f, 1, 0.25f, // back
1, 0, 0, 0, 0, 0.25f, 1, 0.25f, // right
1, 0, 0, 0, 0, 0.25f, 1, 0.25f, // front
1, 0, 0, 0, 0, 0.25f, 1, 0.25f, // left
1, 0, 0, 0, 0, 1, 1, 1, // top
1, 0, 0, 0, 0, 1, 1, 1 // bottom
}));
[/java]
It appears that the coordinates start from “bottom-right” and go around the faces counter-clockwise, with each number being a UV - so the first row above is the UV coords (1,0), (0,0), (0, 0.25), (1,0.25) - one UV coordinate for each of the four vertices which make up one side of the box
The default Box implementation just has each corner’s texture coordinates at 1 or 0, hence the squashing/stretching I was experiencing.