Pat,
I'm definitely interested in a sunroof plug if it provides significant weight savings off the top of our cars.
Other deciding factors for me will be how difficult it is to install and price.
Here's one I found online for a Honda Prelude:
http://www.macqc.com/raceplates/newProducts.htm
Weight savings are significant, it looks great, price is about right, but the installation is difficult. From what I understand, you have to drill 20+ holes or so in the car's sheetmetal.
If you can come up with an easier way to install the sunroof plug and still achieve the same amount of seal, that would be ideal. If you can re-use factory threaded holes and don't require extra drilling, that would be ideal, but I don't know if that's possible.
Perhaps once you get more details on your setup, you can start a new thread about this?