Making soundproof "plugs" for windows

[Jason James]

Hi there, recently I posted a similar post about how to minimize sound going thru windows. I was planning on making the soundproofing permanant by putting a layer of sheet rock, then sound board then another layer of sheet rock in the windows and sealing them up with caulk. This should bring the STC to around 30 which is where my walls should be. HOWEVER, I think I'd like to be able to take these things out realitivly easily. My old plan won't allow that. Anyone know a good way soundproof windows that is removeable? Keep in mind I need somewhere around 30 STC. Thanks

Jason