Well, here we are talking about different gods. I would not ever pretend to be able to prove the god Mac is talking about, for example. And in case that sounds like a shot a Mac, I know virtually nothing of Bgrads version either. In my view, those ideas of God don't measure up. But.. that's just my IMO.
So, when I speak about God, the Creator God, I actually DO believe in the infinite number of things which exist as you mentioned... Multiple universes.. which, I guess are becoming something of a mathematical certainty these days among those folks who think about that sort of stuff.
For me, it really just gets back down to the answer to a question... how did we come to be here. As I've said before, I try and find corollaries in the world. I have NEVER come across a thing which was not created. Ever. And so I have a real hard time wrapping my head around the idea that the universe is here at all, if it wasn't created somehow.
Now, you can say, "Sure, but what about God ... shouldn't he have been created?" and my answer to that is, No, it's part of his very definition.
That said, I have some pause in not just saying "Well, maybe the universe (or the infinite number of them) are omnipresent by definition" I can't really prove otherwise... after all.
Still... I tend to see things as iterations of itself. Much like the old Animal House pot smoking scene... we may well be the dust under the finger nail of some larger being. And, frankly, that's sorta how I view reality... we are God.. Much the same way as some random blood cell is me... It's just not ALL of me.