Understanding the Rationalizations
The most common rationalization for the lack of scientific evidence is the "God must remain hidden" argument. See this proof for details.
Many believers try to rationalize God's existence by saying something like this: "The existence of the universe proves God's existence. Something had to create the universe. Science has no explanation for the universe's creation. Therefore, God created it."
The way to understand that this is a rationalization is to look back in history. Ancient people, before they had science, explained many things that they did not understand with "gods." There have been sun gods, thunder gods, fertility gods, rain gods, etc.
The Bible works the same way. It tries to explain many things that its ancient authors did not understand by attributing them in God. For example, if you read Genesis 9:12-13 you will find this:
And God said, "This is the sign of the covenant which I make between me and you and every living creature that is with you, for all future generations: I set my bow in the cloud, and it shall be a sign of the covenant between me and the earth..."
This is the Bible's explanation of rainbows. Of course we now know that rainbows are a prismatic effect of raindrops. In the same way, Genesis chapter 3 tries to explain why human childbirth is so painful and Genesis chapter 11 tries to explain why there are so many human languages. These are myths, nothing more.
In the same way, Genesis chapter 1 contains the Bible's creation myth. The creation of the universe and life is attributed to God. We already know that God had nothing to do with the creation of life (click here), but religious people still try to attribute the creation of the universe to God.
The fact is, God had nothing to do with the creation of the universe, in the same way that God has nothing to do with the sun rising or rainbows appearing. Science does not have a complete explanation for the universe's creation, yet. While it is true that science does not yet know everything there is to know about the universe, scientists will eventually figure it out. When they do, what they will find is that nature created the universe, not an imaginary being.