First and most important when installing an RO... do not use a saddle valve for the water supply. Use a proper T or an angle stop with a fitting for an extra water line.

Second, liberal use of these makes servicing an RO really easy... especially in an emergency

Third, you can use readily available cable clamps (like for DirecTV or the cable guy uses) for the PE tubing

There are these...

and these...

And the old standby available at any hardware store...