I prepared my house to put on the market a while back and dutifully packed away all my shells. I left the solid projectiles out, but I understand the fear of some nosey neighbor on a house tour freaking out and causing lots of trouble even though all my projectiles are safe as well.
I am not sure I would feel compelled to coat projectiles that are stable and have been for a long, long time. I have a lot of early pick-ups and non dug shells that are nice as they are and I see no reason to coat them. Now I don't live in the same environment as David does (he lives on the coast) and that could be a factor. Also, my stored shells are now in a nice, cool basement but some places like Texas or coastal areas don't have basements.
The ones I did pack away I started crating them. I made wooden crates from plywood that look like ammo crates and lined them with the foam padding that goes under rugs. I wrapped each projectile individually in old linens, towels or socks and put them in there so they wouldn't roll around.
I have a lot of projectiles, however, and this crating business became a pain in the neck. After 8 or 10 were made, I met a fellow who has a small dairy business and he had no problem giving me all the cubical and bigger rectangular milk crates I wanted (sometimes small quantities of beer was exchanged back). So, I started using these in a similar packing fashion as above, except I cut out a piece of plywood for the bottom of each plastic crate so the projectiles wouldn't deform or break through the bottom over time.
Unfortunately, since I packed them up I have had reason to go through the boxes a few times and that too is a pain in the neck. Last time I went through them, I made tags on index cards for each crate and listed the contents.
I guess what you ultimately do will be driven by circumstances such as the environment and quantity of projectiles you have to store. This has worked ok for me so far.
