[JRTJH]

As Wyldfire said, if your water heater was/is empty, the pump will have to push either 6, 10 or 12 gallons through the system before you'll get any significant water flow at any faucet. You'll get some sputtering but no water flow. If, on the other hand, the water heater was/is full, then you may have an air leak in the supply line from the fresh water tank to the pump inlet. Usually there's a strainer on that line (at the pump inlet) and if that is leaking or has been cracked by winter freezing, that would be the source of your problem. If you know where the pump is located and have an "antifreeze line" to winterize the trailer, place that antifreeze suction line in a bucket of water. If the pump pulls water that way, your problem is an air leak in the tank/strainer/pump line.