Coatings are obviously the utmost in protection, but on my older DD with less than perfect paint that stays outside 24/7, I'm staying with lower cost sealants.
Last winter in Western PA, I did a cleaning pass with DG501 in late September, then topped it with DG105/601 and Collinite 476 in late October. I went well through spring with protection still intact, finally polishing with Meguiar's D151 and applying more DG105 in May, just 'cause I felt guilty.
I've tried a few combinations, all involving a Collinite product, over the past 4 winters, but the 105/601/476 combo outlasted any others, so that will be what I repeat this fall.
Bill