Have you ever seen a megavolt power line? Note how far apart the wires are. They are actually a bit farther apart than they really need to be because it is designed to tolerate a large bird with spread wings, but they still need quite a bit of distance. I believe you can tolerate a closer spacing once you're out in space and have no possibility of a plasma arc.
Indeed, I have not, however, I have looked up the breakdown voltage of vacuum at those altitudes, as long as the graph wasn't completely fictional, in that part of space even just 2 cm (barely, but it does) support a megavolt.
