Oops, sorry, wrong forum.

Never mind :)

IMO, probably the best thing you can do is dig a hole and plant it, pot and all, for the winter. Leaving it in the pot above ground outside runs the risk of the roots being severely frozen and killed. When insulated by soil around it, the freeze is more gradual and the roots have more time to adapt. You could also put some straw mulch around it to give a bit more insulation. Second-best solution sounds like the glass-in porch.

I put my potted ginko outside for the winter and it survives snow and freezes. Keeping a potted gingko in too warm of an enviromnent during the winter will actually kill it. They need a cold spell for their normal dormancy and in the spring it sprouts again. Gingkos survive winter snows on Hokkaido Island in Northern Japan just fine.