What you are proposing makes sense, but it seems like a lot of work to get the effect you want. Why not merely set a max limit on how many BTGs you may have for each vehicle type and possibly re-evalute the cost to build each BTG component. The max limit could represent the fact that although the BTG causes no relative mass increase, the basic hull of any ship still needs
some percentage of non-BTG material to provide the skeletal framework.
But then again, I kinda wish no one had brought the darn thing up in the first place... I really enjoyed those darn BuckyDrones...
Combat Squirrel