When I got my 14 Seneca I transferred to it a system that I initially bought at Camping World and installed on my last Class C, it was called the "Extend-a-Flow/Extend-a-Stay" system. It has a manifold that installed between the propane tank's outlet and the regulatory. It allows me to hook up my Weber Q and feed it or any other appliance that uses the same fitting as a disposable propane cylinder. It also has an inlet connection so I can "feed" my system from an external propane cylinder instead of using the onboard tank propane. The kit came with both hoses (to supply and to feed), the feeder hose to an external appliance is about 10 feet long, the supply hose is only about 6 feet.
The manifold took about 2 minutes to install. Shut off onboard tank, use stove to bleed propane, unscrew regulator from valve, install manifold to valve, install regulator to manifold. Turn propane back on and check fittings for leaks with soapy water.
Is this what you are hoping to do?
2014 Seneca 37TS
Toads: 2014 Ford Explorer Sport or 2013 Ford Focus ST