OBXcamper wrote:
Amazon,
Hose
Adapter
Or a welding supply could probably make you one.
Be aware, there is a color coding on the knobs for propane lines. The line in the Amazon link above, has a black knob.
Look at OP's picture, you'll see his horizontal tank hooked up to a line with a green knob.
Those color differences are based on flow rates.
Black -- Low flow commonly seen on BBQ grills and small space heaters.
Green -- Medium flow commonly used on RV's
Red -- High flow commonly used on large space heaters / furnaces.
I learned this by doing exactly what OP intends to do. That is a vertical tank sitting on the ground, with a hose and adapter going into the camper propane system. It worked as far as lighting a small flame on the stove, but, there was not enough gas flow to operate more than one stove burner. The water heater and furnace would not operate at all.
Changed that black knob (AKA handle, AKA ACME nut) to a green one and all is well.
I purchased all the parts on ebay or picked them up at Ace hardware, and made the line myself.