It seems to me it would take a huge snow load to damage an RV roof. But I can see snow melting to some degree and running into crevices or vents, or re-freezing and thereby cracking something. I did try to remove a particularly heavy snow once, and I had lots of trouble, not to mention the extreme danger of climbing around up there. I say keep the vents shut tight to avoid or lessen water infiltration and let warmer temperatures or that low underpass to remover it.
2011 Sabre Silhouette 260BHS
2006 F-250 6.OL