I have fitted Gemini inner tubes to a Tornado rib.
If you follow the instructions they are reletavely easy to fit.
The only problem is that it does not state on the instructions that when they are inflated they MUST be very, very hard.
After I hade fitted them and used it for the first time they split near the transom, Gemini explained that as they were not hard enough they rubbed against the inside of the tubes, they took them back and repaired them, when I got them back I fitted them.
When you think you have put enough air in, just put more in until they are absolutely solid, this way they will not move inside.