I've done the JB weld beads on intercooler pipes in the past. Just scuff the end of the tube where you want the bead, clean it good with solvent to remove grease and oil, then use masking tape to outline both edges of the bead and apply the JB weld. Pull the tape off before the JB weld hardens. Make sure you use the quick setting JB weld and keep an eye out for running. The long cure JB will run and you will have to keep turning the tube for over an hour to get a nice even bead. Also, don't put the bead right on the edge of the tube, leave an 1/8" or whatever, so you can get your couplers starting on the tubes. This method is easy, cheap, looks good and is very durable. Sounds perfect for your situation.