The cover started out as a fitted mast-down storage cover purchased from International Marine in 1997. My local canvas-smith modified it so it could be used for mast-up storage as well as mast down storage.
My local canvas smith modified it for mast-up storage by installing the zippers and hole to go around the shrouds, cutting a hole for the upright mast, and cutting holes for the backstay and forestay. He cut a hole in the front for the CDI to stick out of when the mast is down and also made a 5' sock to cover the furler. The sock protects the sail against chafing when trailering and to protect it from rain and mildewing if you store the sail on the furler.
I forget exactly how much it cost, but I think he charged me about $800 for his labor and about $100-200 for materials. It was expensive to have him modify it at $50/hour plus the cost of zippers and sunbrella fabric, but it was still cheaper than having one made from scratch.
The price of $675 for a fitted cover from IM is VERY good, compared to having one made to order. It take many hours to design the basic fitted pattern from scratch, and IM already did all that for us. I piggy-backed on their design, so to speak.
My cover is very complex since it works for both mast up and mast down storage,
and I would expect a local canvas maker to charge around $2000-2500 for something
similar if he had to design and fit it from scratch.
The cover can be used with the mast up, either on the trailer,
in a slip, or on a mooring.
For use on the water, there are weighted "sandbags" that clip onto the bottom of the cover.
On the trailer, I use bungee cords to hold the cover down.
The cover works with the mast down too. You can see the roller
furler with the sail on it sticking out the front.
There is a "sock" for covering the furler and sail, but it's not in this picture.
In the picture below, you see the mast sticking out of the cover
at the stern.
You can also see the opening for the backstay (trimmed in white) which is used when the mast is up.
In the picture below, you can see the opening for the furler,
used when the mast is down.
In this picture, the mast is up and you can see the headsail sticking out through the cover.
The picture below is a close up of the zipper just aft of the mast, which is used for mast up storage.