Any hydrophobic coating will be compromised by dirt and grit. Car wax has worked for me--and might very well work for you, too. The trick is to keep your topsheet free of dirt and grime (a high-gloss topsheet helps, of course). Clean it thoroughly first. Then apply the wax (or rain x). Buff it occasionally to remove any dirt, film, gunk, particulates, etc. Without these surfaces to cling to, snow will simply slough off the deck. Or at least that has been my experience.