Hose between propane tank and regulator?

A commercially produced pigtail has a built in check valve that stops the flow of propane in the event of a break in the line. These are manufactured for the purpose you need. Go to your nearest RV parts place or propane store and buy what you need, install it, and go camping while feeling safe about your LP system. I found up to 60" pigtails in the catalog and they were less than $20. One end has the proper connection to attach to the bottle, the other end has 1/4" threaded connector to screw into the regulator. The safety of yourself and those around you is worth more the anxiety of wondering because you tried to save a couple of buck by cobbling something together. Problem solved.