I found something that works as a cab-only cover. It's an extra large ATV (4-wheeler) cover measuring 85x48x40 inches, available for $25 at Checker/Kragen/Schuck's auto parts and elsewhere. Smaller sizes do not fit. I use it to keep my tintop windows from icing over, and it saves a lot of scraping and cuts down on fogging.
Probably fits soft-tops even better, and I know from long history that a cover keeps your soft top looking near-new for years. Use the cover year-round--it's a lot cheaper to replace a cover than a soft top!
Thought you might like to know!
-=- Roc Doc in Idaho -=-