I believe the hose is 3/8" but I'm not 100% on that. I got a deal on it at a local ma and pop RV repair place. The entire set up; PL, reg (actual RV regulator, not a BBQ grill job), hose, and hose fitting for the pipe all brand new and assembled (except for the flare fitting for the pipe, it was hand tightened on the hose and the MPT end was capped off), only $30.
One of those times when seeing exactly what you need with an inch of dust on it, and saying "Hey, I'll give ya $30 for that." actually payed off.