I only have to deal with maybe 18" of snow during a bad storm and temperatures down to the single digits occasionally, but I go to the local Lowes/Home Depot and get a heavy duty tarp to pull over the camper in the winter. I don't worry about breathable as the vents/domes on the top of the camper will keep an air gap there for ventilation unless there's enough snow pack, but breathable wouldn't help then either. Cost $40-$50 and generally only good for one winter, but IMHO, better than the snow/water freezing and thawing it's way into any gap it can find. To lash it down, I stretch a cord between the front and rear jacks, then run loops (VVV) through the grommets on the tarp and around the cord tied between the jacks. Better then bungee cords all over the place...
Really gotta get that "shed" built...