Hi Scott,
I made what Doyle Sails calls a 'Stack-pack'. I includes a lazy-jack system for managing the mainsail as it is lowered, and a mainsail cover to protect the main from the sun. The stack-pack mainsail cover in made of fabric that is held in the boom track/slot along it's longitudinal center. The fabric is taller near the boom (about 2') and has 1/4" dia fiberglass rods installed in the hems which are tied to the lazy-jacks.
I hated both the lazy-jacks as the mainsail would become entangled in the lazy-jacks during both raising and lowering and the mainsail cover didn't work as I hoped and got in the way of setting and reefing the mainsail. I ripped these mods off after the first sail with them.
I maid another mainsail cover, a standard design, but it didn't come out nice since I re-used the stack-pack cover and had to sew extension panels to the front and rear of the cover. I works very well but looks a bit rag-tag.
I suggest you download Sailrite's instructions for making a sail cover, I haven't read it but I'm sure it's better than anything I would write (13 pages for $5)...
http://www.sailrite.com/Sail-Cover-Instructions-Downloadable
Hi Danny, Using the roller furling boom function for storing the mainsail is a great idea. I would do it except I have a center boom mainsheet and slab-reefing (jiffy-reefing).