I use barb fittings that are 1/16” larger in diameter than the I.D. of the my gas and liquid lines. Chill the fittings in the fridge and soak the end of the tube in hot water for a few minutes and the two go together rather easily.
Some folks claim that when the tubing cools and shrinks it makes a leakproof seal; I’m a belt and suspenders guy. I put a clamp on each connection. I prefer Oetiker clamps; I think they make a neater installation. Any appropriate style of clamp will work, however.