On my 192, I'm able to remove the 4 lifeline stanchions, and use the lowered mast as a ridge pole for a tarp. It's tied to the bow pulpit, with a cross brace just behind the cabin, and one at the transom. The middle brace at the cabin does an amazing job of supporting the mast, and preventing any downwards flex of the mast. Last year, I bought a 12x25 UV resistant heavy duty silver poly tarp, and it's still in good shape (it ought to be) for maybe $50 shipped. I have that tied down securely at roughly every other grommet, down to the trailer. If you can't remove stanchions, it's best to build some framework to prevent the tarp and snow load pushing the stanchions inboard. You can do this with PVC pipe. Some folks have wedged grey electrical PVC conduit into the trailer frame, and bent them up over the boat so it looks like a conestoga wagon.
I heard about this place,
http://www.shipshapecanvas.com, so I asked them if they have made any covers for the 192, but alas, they have not. However, they can make you one if you mock up a template using plastic sheeting. There are probably many other companies making winter covers, but ShipShape is one I heard of. Rudy at D&R might know of a place that already has done a 25.
Brian