Did this just start happening? It's hard to say how long the air will last. Have you check the valves in the stems? Do you hear it leaking and have you tried using a spray bottle with a mixture of dish detergent and water? It will bubble at the leak area if you spray enough solution on it. The mesh is a protector against the line rubbing on anything. Is your warranty still good, call yor dealer, they may be able to check it or advise you where to take it. If it's not a valve stem that needs tightening, you can take it to a Ford Truck Center and have them check the tire for possibly a nail or a bad valve stem.
2007 Georgetown 370TS
aka - RAYNMKR