Snow and Ice melt from the bottom, not the top. So a nice 40 degree day will reduce the height of the snow and all that melting water will seep into any crack that it can. Night falls and the temps drop back to below freezing and that water will refreeze causing expansion in any crack or crevice it can find.
I'm an advocate of winter covers and cleaning snow off when it is safe. Dark colors cause melting more than light colors. Just my thoughts after running a marina for the last 25 years and having boats or trailers for the last 40 years. Your results may vary.