A properly made propane hose with 1/4" NPT fittings is cheap and made for the job. I would not try and save $20by jury-rigging something . High Temperature Tools and Refractory ( The old Ellis refractory) carries them up to 30 feet long, IIRC. I also recommend using the quick disconnect fittings. They allow the propane hose to be moved from one device to another easily, as well as allow un-hooking the forge from the tank in seconds. Really great for portable rigs that go to demos.
Just a note, but make sure your regulator is the type for a forge. A BBQ regulator won't work.