I'm not aware of any Coaches coming with a factory coupler for an external barbeque. I think a previous owner must have installed it - which means it could be any brand/size.
This is type I installed on my Coach. https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
On my setup, the 25-ft flexible propane hose (also from Amazon) comes off the factory line that feeds the cooktop (and refrigerator if you don't have a residential fridg). Since that propane is already regulated by the Coach propane regulator, you need to remove the regulator that is on the barbeque now (you don't want to regulate the pressure at the RV and at the barbeque).
I also use the Weber Q. it is not difficult to remove the regulator and install the quick coupler. I just coil up the hose in the basement when not in use. You could also put a disconnect on each end of the flexible hose if you don't want it permanently attached to the coach.