This may only be a partial solution to the problem, however, since the types of things you will want to teleport (I'm looking at ore and refined metals) don't teleport through portals. Unless I am completely misunderstanding the label they have on them. Which means portals would be useful for things like foraging or initial travel to a location, but carrying ore or the like back is a manual task. I'm also not entirely sure if they will come under attack in single player, either.