Yes, the dry storage is good to mention, but the photo is the most important thing. The notion that it hasn't been ridden for n years is a negative if anything - better to go ride it and see if everything works. Then you can take photos out on the trail and that is way more credible than in your back yard, because the buyer can see they can go straight out on it, and buying it won't be the start of some mega restoration before they ever get a ride.
Mention the condition of the frame and the paint - if it's straight, no dents, no cracks, no rust, not much stone chips, then say so. If it retains its Tange Ultimate Ultrastrong sticker, take a snap of it (the tubeset is a custom mix of Tange Ultrastrong, Ultralight and Concept).
Also mention the condition of the Manitou - if it isn't solid, you really have done a good job of preservation because most of them are. Elastomers don't tend to survive 15 years too well (sad to say, but the Marzocchi would have lasted better, being an air fork!) But the main thing is the frame is suspension-adjusted, so the new owner could replace the fork with a more recent shortish-travel one if desired.
Best of luck