I was thinking of putting the nylo flow tubing in side a lager Dai Plastic tubing 3/8 maybe even 5/16 that way I could replace the 3/16 tubing rather easily ,With out distruction to the wing.I can not see any problem with your idea, other than those you mentioned. But I'm not certain there is any reason to expect much wear to the nylaflow within the wings. There will be wear, however, at the inboard end of the nylaflow, where the rudder cable makes a 45° turn. If you install a pulley in that location, your nylaflow will <probably> last forever.
Just my opinion, keeping in mind I still haven't flown my Velocity yet.
SW RG TopDoor (Classic)