Don't seal it. Over time, gas will break down the sealer and it will end up in your carb. To prevent internal corrosion and rusting, keep the tank full of gas. Since it's going to be a new tank, use ethenol, it helps with moisture. Also, make sure you have a drain in the bottom of your tank for removing old gas if it gets stored for long periods of time.
Just my 2 cents,
Scott
