Well, I have gotten some really good advice from Paul T. He recommended cutting the glue with toluene and painting it right onto the exposed fabric, putting on a few layers, letting it cure for ~24hrs, and then repairing on-top of that. I didn't really have the highest expectations of success, but alas, it worked and has been holding up really well for 5 trips now! I think it is absolutely paramount to have and maintain full pressure in the tubes when running the boat. All three times I broke a cone, I had another slow leak somewhere else that caused pressure to drop, and I was too lazy to top it off before heading home. I think that running w/o adequate pressure causes the tube to be thrashed about much more, putting additional peel stresses onto the overlaps and tearing it apart. Thanks Paul!!