Made some progress at last. I found after too many hours of hacking stuff around that this:
uniform sampler2D texture0; //Random Surfaces
uniform sampler2D texture1; //Random Greys
needs to be "texture" and not "iChannel"
With that, I was able to use texture1 to create a random starting number BUT it has screwed up the texture on texture0 in the scene.
If you load up the attached scene...
http://bit.ly/3XVcSZC
You will find 2 versions adapted from ET431. In the RandomCave version, the "cave" that is shown is different every time i.e the random number is being generated but the textures are all messed up.
There's a second NonRandom version to see what the textures should look like but in this version the shape of the cave is always the same.
If anyone knows if/how I can fix these textures ....
👍