Stack-Packs were a huge improvement on a 64' ketch I used to work on. For that particular boat, we got them to prevent having to crawl out on the booms (either over a giant center cockpit bimini, or over an aft cockpit about 7-8 feet below) to wrestle sail covers around the lazy jacks. As such, the sails were much better protected once Stack-Packs were installed. 

A surprise benefit was that it was possible to walk/crawl out to the end of the boom inside the Stack-Pack, even while underway, presuming there was at least one reef in a sail, or if it was lowered completely. (I can't remember what made that necessary, but it was a couple times.) 

The big, heavy main sail on that boat dropped right into the pack, as intended. The mizzen was close to the size of a W32 main, and we found that the weight of the sail alone wasn't enough for it to reliably tuck itself fully into the pack when being lowered, so we'd still need to do a boom walk afterward to get it settled, but it was much better than before, and took less than a minute. With a Westsail boom being easily reachable from deck that wouldn't really be a problem, but'd be worth anticipating. 

Do you already have lazyjacks on your boat? If not, do you wish you did? My K32 doesn't have them, which I'm fine with, and at this point the simplicity of just a sail cover outweighs the complexity of a Stack-Pack, even though I'm sure my sail would benefit from being covered more often, too. But if I had, or were thinking of adding lazyjacks at some point, the Stack-Pack would start making a lot of sense to me then.

I built a Stackpak for Tamzin some years ago before they were very common.  It was a seat of the pants thing and I loved the way it worked but unfortunately it didn't last that long (my workmanship).  The next version I made using the basic instruction video from Sailrite with a few modifications learned from version 1.  It has held up very well and functions perfectly.  As noted in the previous post you still have to pull the sail down and lay it out within the stackpak but that takes all of a minute or two.  It is by far a much better solution than the old sailcover in ease of operation and protection for the sail.  The Sailrite instruction video is free just go to there website and look it up.

Aaron Norlund made his own.  link to an album.

and here are some sailrite links

16ft boom  http://www.sailrite.com/Sail-Pack-Stack-Pack-Kit-for-16-Boom

and a video... http://www.sailrite.com/How-to-Make-a-Sail-Pack-Video

I am also coming up on the time to redo the sail cover, and had thought about the stackpack but I have not found any good pictures showing the lazy jacks stowed when the sail is up?

I do have lazy jacks and they are ALWAYS stowed when the sail is up or when it is all down. i.e. I only use them when lowering the sail, for which they do work great! (stowage or deploy takes about 12 seconds or less per side) any more than 20 sec. would be hard to accept. Granted sail ties and the cover, takes much much longer.

Has anyone found a good solution to stow the jacks and canvas while sailing. I have some Ideas, but not sure they would be worth the effort. And the ideas may be, no better than my current sail cover design?

The ideas I have, include a bronze wire support (holding the stack pack up and in a u form just aft of the 2nd reef, so as to support the outboard ends) . The other thought was having the lazy jacks use a pickup line (when deployed the jacks would be lifting the battens just like in the pictures I see where the jack is attached to the batten) but when stowed have a slack line to the batten.  i.e have the batten stretched between the wire support outside reef #2 and a cleat on the mast to have a bifold in the front of the pack.

I just do not likesailing with the jacks up!  (chafe, sail shape, boom lift, windage as well as line entanglement).  

And thanks Jay for the links to Sailrite and Aarons work, that is nice, but (I think they are sailing with the lazy jacks deployed?) this link is a bit closer, but not quite there, for me. http://macksails.com/mack-pack/