Can you use interior paint outdoors and seal it to make it weather proof?

No, most interior paints do not have enough freeze-thaw flexibility nor UV resistance to be used successfully outside. If you seal it with an exterior paint, that will take care of the UV issue, however you would want to seal it with a 100% acrylic primer, then coat it with a high grade paint to overcome the freeze-thaw problem.

Neither interior nor exterior paints are weatherproof, only weather resistant.