The two ways I have done domes are:
Use a hammer to form over the ends. I did this cold against an anvil. I have cut slots/darts out of the end to better fold the metal. Once formed then slot for the drop out. Fill/coat with filler during brazing and file away. If done well the filing won't be much.
Fill the tube end with a steel plug, use brass/bronze, then grind/file the dome before slotting. This method takes longer but claims of "skilled technique" made in your blogs will be more believable
WRT cleaning the stay insides I do it before any of this and trust the flux. Andy