If you're going to buy an aircraft cover, I would suggest getting one with silver laminate. Normally aircraft covers have the fluffy plush stuff to protect the paint/windows, however that fuzzy plush stuff collects dust, grit, etc., and will eventually scratch the hell out of your windows. Silver laminate does not do that. In fact, during Operation Desert Storm, the military had to switch from the regular plushy fluffy fuzzy crap to the silver laminate because of the constant sand bombardment.
You can find covers to cover the entire surface of your mooney from http://www.aircraftcovers.com/. They are also known as Bruce's Aircraft Covers. If you tell them you're interested, they will send out a full binded information packet. It has samples of the materials that are used (I think it does, I can't remember for sure) and detailed instructions on what measurements to take and how to take them. Return the forms to them and they'll start sewing your aircraft cover.
They have canopy covers, extended canopy covers, wing covers, tail root covers, etc. You can really cover your entire aircraft if that's what you want to do.
The fuel cap covers I was looking at were for the Cessna/Piper group. Looks like you're out of luck on that one. My fuel cap was leaking and just yesterday I switched out the o-rings. Solved the problem right up. Instead of using a -338 I used a -339 for a tighter fit --- worked like a charm.
Good luck,
Nishant