Yes, 1/8" copper tubing can be used...kits available at most parts houses. I've used the plastic lines without any problems and am currently running the copper line in my 235. Can't envision a 235 developing enough pressure to "blow off" a tight 1/8" line.
The same CONE SHAPED ferrel, is used on both the plastic and copper lines. It is slid on the line...the line is pushed down into the female fitting approximately 5/16" and the nut is tightened, snug. Once you snug down the nut....the CONE SHAPED ferrel locks and can not be removed from the plastic or copper line.
Be sure to push the line down into the fitting so the CONE SHAPED FERREL can get a good grip. Oil spray down around the exhaust pipe is an invitation for disaster. Hope this helps.
Dave
