Thank you, Sacha.
I just received a couple of 12.5mm tubes.
One with rigid foam (3.1oz), one with soft foam (adds .3oz to the overall weight of the tube- 3.4oz).
However, the weight is more towards the tip end of the tube. I will probably hollow this out some in order to balance the weight out.
The tubes are very smooth, straight and have a good finish. They are definitely worth a try.