Chief,
I made my own from a heavy duty tarp last fall. Set snaps in the stock hems for the forward edge. Hemmed the aft edge with permanent double-sided carpet tape. Loaded the aft hem with closet hanger rod stock for some weight, then clamped that edge down to various boat features.
Key is to keep storm weather from getting under the edges and lifting the covers. Cover really helped during a big snowstorm event last December. Cost maybe $30 plus a good snap kit off the internet. Sorry no pics, the ones I've got just show a foot of snow on the bridge.