Worse than the scratching is the fact they trap moisture, then become a sauna on sunny days. This can/does quickly and easily destroy the clearcoat.
OP, skip the battery tender too. I spent 3 decades as a motorcycle mechanic, I've seen hundreds of batteries killed by those things when they were left plugged in full time as people over-winter their toys. I know, the advertising all claims they go into "float" mode and won't do that... you always believe advertising meant to sell you a product? Even the best of the new generation (read, not inexpensive) battery chargers can/do/have killed batteries left on full-time connections. One day a month is Plenty to keep a battery ready to go anytime you want to drive. Or, simply drive the vehicle for 30 miles or more one time a month (if you're not going 30 miles or more, don't bother to start it as you won't give the oil enough time to cook off residual water and byproduct acids from combustion, instead you just spread it around the engine ~ and prolonged idling is even Worse than not starting it).
I have 4 vehicles between 2 people here. Only 2 covered spots, though I'm working on adding 2 more. Keep the sun off the paint is the #1 thing you can do to keep it looking good, but that only postpones the inevitable. Keep a good "wax" (some sort of paint protection) on the vehicles, I'm old and like actual wax so it's something I apply every 3 months. And drive the vehicles once a month for at least 30 miles (well, that's good for non-winter states, if you're trying to drive on a day when the high is only -10f, you probably want to up the drive time by double). I use all the systems of the vehicle on those drives too, A/C, Heat, window washers, 4wd, etc... anything not used tends to deteriorate faster. I have an expensive battery charger/tender (that has a couple "restoration" functions too), I use it once a Year just as a preventative thing. Try to correct any potential damage and prolong the battery life. 8~10 years out of a battery is normal for me... well, had one car that needed one every 5~6 years lick clockwork but that was the norm for that car across all owners.
