Lisa,
Have you asked or checked with the storage owner if there has been any breakins or attempted breakins recently, I may be wrong but it could be eith an attempt at getting in the van as im sure you would have noticed it when you put the van back in storage after your last outing after checking all windows are secure. I can't see this happening with traveling back on your last outing unless it was hit by something but the large split you say is on the inside and small crack on outside, not sure what anyone else thinks about it, but I would ask the site owner just incase other vans have been possibly damaged.