And this is my point. There wouldn't necessarily be any Gs because if there were Gs there would be motion and if they moved they would exit the space/time they're in. I'm sayings they are stationary and they're manipulating their local space time to move without motion. There wouldn't be any Gs. This form of travel has been speculated as a means of traveling faster than light because it doesn't actually require any velocity at all. It works by contracting space in front of you and expanding it behind you. Reputable physicists have said it wouldn't violate the laws of physics, they just have no idea how to do it. And this was my point, perhaps the answer is outside our understanding and applying our existing frame of knowledge to these phenomenon will be asking the wrong questions. Perhaps it's not a question of how do they withstand the Gs, perhaps it's how do they distort space without generating lethal heat/radiation etc.
This is just pure speculation on my part and I'm not even saying that this is what I think is happening. It's a thought experiment that illustrates the wild nature of the unknown. Ancient people, or actually just people from 200 years ago, would not understand our phones. For starters a capacitive touch screen doesn't make sense without an understanding of electricity etc. I think we're seeing a technology that we don't understand.