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I hate those homosexual looking things, There's no real proper way to secure 'em onto your car, Double sided tape (No matter how strong) will not fare any better against a thief that really wants it.
I am not sure how it holds up on the back there, but I had eyebrows on one of my BMW's and with the Arizona heat, after a bit the double sided tape gave up the ghost and I lost one on the freeway. I would look for something stronger in Nevada.
My window visors were held on by some real sticky stuff that looked like foamy silicone. The heat here in Laredo, Texas is nothing kind and they hold up like champs even at 90-110 mph on the loop during summer days. Then again, their surface area of sticky contact is probably much greater and have less wind resistance I'd imagine.
I believe they are used more as rear sun shade for the rear passenger area than as a spoiler. At least that's how many of the older cars used them, like the mkII Supra.