I don't live in an area with that much snow (not that 400 inches falls at once or survives the whole winter without some melting in the high-altitude sun). But I store a boat outside using a heavy duty poly tarp and creating a frame with a ridge beam that creates a steep pitch over the boat. A 4x4 at the front and back of the pup with a substantial (2x6) ridge beam would do. I use rope to stabilize the ridge beam. I tie the rope to the perimeter of the boat, which you could do on the pup. This will create a steep pitched frame, over which you put the tarp. Fasten the tarp very tightly around the sides of the pup. This will prevent snow from accumulating that much before sliding off. Worst case is that I hit the tarp a few times to encourage the snow to slide off after a heavy snow. Make sure that the tarp you consider is wide enough to create a steep pitch, and use the grommets to tie the tarp tightly to avoid any sag on the sides. You will be fine.