No, I'm not offended. If I'm being a bit nippy it's in frustration that I'm not managing to explain myself well enough.
I think to explain how I think God can intervene, I'd have to try to explain how I picture God and the universe to start with.
I think that the universe is inside God, and that God is all through everything in the universe. If you picture the universe as a sponge and God as a bucket of water, that would be close. So the sponge is inside the water, but the water is also inside the sponge. Actually you probably ought to try to get rid of the bucket from the image, as that leads to questions of what the bucket is made of and what's outside of it
But then you have to imagine the water all staying in place without the bucket... it's not a great analogy, but it's the best I can manage.
So God isn't outside of the physical world, but an integral part of it. As to how God could communicate with humans, I think that the communication is either a part of the universe that we can detect but not really understand, like the background radiation, or something that we can theorise about but not detect yet, like the Higgs-Boson particle, or something else that we haven't even theorised about yet. But it would be a part of the physical universe, not something "else".
As to why Camping was wrong - well, it's not simple, since if I believe that God can communicate with humans (imperfectly but noticeably) then I have to say that either Camping thought it was God speaking but was wrong, or that he misinterpreted what he heard. In mainstream denominations, people are encouraged to weigh up what they think God is saying to them against what the church as a whole teaches, what the Bible says, what their reason and morality tell them. And if what they think God says totally contradicts everything else, then they should think very carefully about it before acting on it. I dont believe that, if the end of the world was coming, God would tell one person about it - it would either be a complete surprise for everyone (most likely), or would be signposted in a way which did not leave any room for doubt (less likely). For one person to decide that God has told him alone something so important for everyone is massive egotism, and ought to make them think "Hang on did I get that right?"