ksg5000 wrote:
You need to have a mechanic check out the rig - they can pressurize the fuel system and likely locate/fix the problem quickly. Call around - you may find that most shops won't work on big RV's (they don't have space or equipment to lift them) - outfits that work on big trucks will usually take RV's.
While your rigs in the shop have them check out brakes and change fluids etc. Low mileage on old rig sometime means that the basic chassis stuff got neglected (some stuff needs attention because of age vs mileage).
check for visible leaks from the tank to the engine both the pressure and return lines, and if you can also check the vent/purge lines for the charcoal canister. If you cant find anything find a garage that can Smoke the system (Inject smoke into the gas tank to check the vent/purge lines) as it will also show any leaks that may be in the top of the tank, filler neck etc...