We don't recommend it.
For one thing, there's no way to protect them from stinging/biting insects. For another, the temperature varies too widely to make it safe. In NC, it's far too hot in the summer, as they can die of heat stroke at anything above 85 degrees. And in the winter, it's far too cold.
And for a third, they're prey animals, and as such, they can hide illnesses until it's too late to save them. The changes are subtle, and if you're not with them every day, you'll miss them. That can mean the difference between life and death for your pig.
But just out of curiosity, why would you want pets that you don't keep with you? They're endlessly entertaining -- mine lived in my living room right by my recliner. They were far more fun to watch than the TV!