Closing the blinds won't be enough. People will always come in behind you and open them and light gets through most blinds anyway. I UV tented my windows (when I lost the war of the closed blinds to my wife, housekeeper, secretary, mother...basically everyone)...I hope it works. Sadly, it'll be some time before I know.
I'd recommend the UV tent (obviously, I've gambled with it) but make sure you get the real UV tent and not just tent (and don't trust the person you bought it from...make sure it is the real deal and not just tent...).
Also, installing decals is a nightmare. I saw one person attempt it years ago and it was a colossal failure. There is a reason people sell their faded games with uninstalled decals (proving decals means they don't have to take a hit for the faded cabinet, but leaving them uninstalled saves a monster amount of work that could be a total failure, meaning you need to buy more decals).