I think it's a great idea. My car was and still is a radio delete so there is no antenna. It is great not having to mess with an antenna when covering and uncovering the car. And the antenna won't get damaged by vandals or birds. Yes, birds, I have had birds including an owl fly up from the side of the road and run right into them, and they were the power antennas on my Tbird and Cougar.
I am in the middle of a restoration on my 67 and I plan on not putting a hole in my new fender for the antenna. Hidden antennas are just as good these days. Plus the benefit of having an easier to put-on/take-off car cover is nice.