I actually thought of using couplers instead of the tubing, just because vinyl tubing looked inappropriate for the job, but it's been fine for me so far.
If I may suggest to use these: http://tinyurl.com/hcu59py
Don't have to be from the same seller but a 5mm to 5mm should do the trick.
I'm not sure where you would need to modify anything.
It should be a plug and play type of situation.
what's causing the Z rod to slip?