Originally Posted by
rccardr
Cannondale drilled a hole in each side of the downtube, then used a piece of threaded rod and threaded DT mounts (one side was two pieces, so it could be snugged up against the tubing). If you can find one of those mount sets (they are no longer made), you're good. Done properly, it will not compromise the integrity of the tube.
Klein did the same thing on some of their late '90's frames. The bosses were threaded onto a double ended rod that went through two opposing small holes in the downtube. They had problems with failures and Trek (Klein's owners by then) make repair kits that replaced the damaged parts. An older Trek/Klein dealer may have one still in inventory.
Do not even think of having the bosses or anything else welded to the downtube.