Peter, I am not so sure I would, in our club we had 2 of these with steel boilers and copper tubes, and the copper tubes were always leaking, It was thought that these expanded at a different rate to the steel shell, thus loosening the tubes. These can be re-expanded, but eventually the copper will get mighty thin at the tube plates, after continual expanding. Both owners replaced their boilers with new steel ones with steel tubes.
You say you have done it twice over a few years, I know it depends on how many years, but my 4″ Garrett is about to have its second set of tubes, the first set lasted about 10 years, the second slightly longer, as it was not used as much. If your tubes are only lasting 2 or 3 years that does not seem long.
Chris Gunn