I am adding this comment for anyone interested in a project like this. A couple of weeks back i got a mercury inflatable with the original tubes torn, completely useless. I started the project to add fiberglass tubes instead and see what happened. The results in my opinion were great:
It is only about 40lbs heavier than the original boat. It floats and runs just like before. The size is a 3.40m.
If younare tired of fixing and repairing your tube and have the space (trailer), doing this mod can make your life much easier. I had my doubts that this would work, but it does. I still have the positive buoyancy that makes inflatables so great, without the maintenance.
I added some pics from my trial today. If anyone has any questions or comments, please let me know. Everything is appreciated.