Those look great, and will make some awesome habitat.
As a word of caution.....be careful in your choice of scrap material.
I put a beautiful hunk of copper ore in a very large aquarium. It looked just like turquoise, but killed everything in the tank overnight. There was a sharp and expensive learning curve at that point.
Scrap copper tubing is easy to work with, but can be deadly. Commercial root killer, and septic tank root remover are made with copper sulphate. Don't make the mistake I did.
Stick with your poly tube. It's much safer.