pressure relief valve dripping

Well, I turned off water at source. Opened the hot valve on shower which is above the hot water heater, left open until it stopped running and left it open, opened relief valve and left open until drips stopped, then snapped it a few times and finally snapped shut. Closed the shower faucet and turned water back on and turned electric heater back on. Waited a while til water nice and warm and then took shower. Still had some drips when done. Enough to make small amount on ground. So repeated the process and still had some drips. Any other ideas. Maybe normal but it wasn't in other coaches with Atwood water heater. Doesn't drip when not in use. Only when using hot, Any other ideas? Maybe it is just the valve that isn't seating and faulty or I need to keep snapping.