That's pretty much how I see it too. Revelation 13:5-6 says the Beast speaks great blasphemies against God but also his "dwelling place" and "those who dwell in Heaven".It’s practically impossible to explain the rapture away.
Yes initially, Satan might try to use the UFO argument. But honestly as we read in scripture, by the time the seal judgements start rolling, people clearly know it’s God. In my option the UFO tactic from Satan will be very short lived. People will start to put pieces together really quick.
Satans attempt/tactic to hide the existence of God from humanity will finally come to an end. At that point Satan will probably shift gears and try to paint God as the evil being, and that him (Satan), the antichrsit, and false prophet are infact here to “unite the earth”, and anyone who is not on their side is against them. This will explain people complying with the Mark of the Beast. Those who don’t are seen as evil and killed off.
Ever ask yourself, during the tribulation how are people around the entire globe okay with letting the one world government execute people (by probably thousands to millions) who don’t take the mark? How do family members end up turning each other to the government? (As Jesus described).
It’s because the enemy would have succeed in convincing many people God is evil, and any of his supporters are to be killed as a threat to society and progress of mankind.
The big spiritual battle in the last few years has been trying to convince to people of Gods existence. The enemy’s tactic has been to remove the spiritual component of mankind so they don’t buy into any “Jesus” idea. In the tribulation, the rapture and all the following plagues will destroy the idea that mankind came into existence from absolutely nothing and evolved via monkeys. People will have to make a decision. God or Satan?
This sounds to me like he isn't denying God's existence, but instead he's challenging God's authority directly.