Pool noodles are the move seriously. I did basically the same thing with my WRX a couple winters ago and the tarp alone beat the hell out of my old cover. The secret is that airflow thing, you gotta let it breathe or you're just trapping all that wet air right against the paint. I also swear by those DampRid buckets, I used two and swapped them out once mid winter. Only thing I'd add is run a bungee cord under the car if you get high winds, tarp flapping can still leave fine swirl marks if it's not snug.