Yes you can connect most any portable propane BBQ to your RV's main propane tank. In fact CAMCO Manufacturing makes a kit to do exactly what you want to do. It is the Camco Propane Brass Tee with 4 Port with 5' and 12' Hose which is also known as "extend-a-stay" (Pictured at the top of this page). This setup not only allows you to hook up your portable Propane BBQ/Grill but it also allows you to connect an external propane tank to your RV in the event that you run out of propane and you do not want to move your RV to get propane. The kit also comes with hoses needed to connect your portable BBQ/Grill and external Propane Tank to your RV's main tank.
Quite a few RVers have this setup on their RVs. This can be a do-it-yourself job as long as you are comfortable working with propane connections. If you have ever hooked up a Gas Dryer in your home, you should be able to make this modification on your own. If you are not comfortable doing this yourself, you may want to pay someone to do it for you.
The video below outlines the installation procedure for this accessory:
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