I use trays which I sit and make (laboriously) out of say 300micron white
card. I use a standard 30x40mm (by20 tall) size. For any shells too large
for this I make trays to closely fit the shell. This may look a bit untidy,
but it takes up less room than having say 3 or 4 different nesting sizes.
Putting a shell that is slightly too large for one size tray into the next
size up can waste a lot of space. I'm not sure that the amount of acid in
the paper of the tray will affect shells; I think the amount of acid the
paper can hold will be very small and will be quickly neutralized by the
nearby carbonates. Good-quality card shouldn't turn brittle and yellow from
acid decomposition over time, as did many older papers.

I do not like plastic for trays because it's hard and can easily break
delicate lips and apices as the shells roll on opening the drawers.

I must say, I find big steel map/plan cabinets absolutely ideal for
collections. These should have roller drawers; drawers on fixed runners
drop rust, paint dust etc into the shells. Such cabinets can be expensive,
but it is possible to get them cheaply at some auctions of office gear etc.
I've paid as much as $200NZ (=~$100US) for a tidy 5-roller-drawer unit and
as little as $80 for four somewhat scruffy 5-drawer fixed-runner cabinets.
And I got a near-new roller 5-drawer unit free from what used to be our
Geological Survey. Being about a meter square, these cabinets are not too
vulnerable to roughhousing youngsters (perhaps they could be electrified
using an electric-fence unit?)/

I also have several particleboard map cabinets. I have fossils in some, and
these have been OK, but some Recent shells in identical cabinets have
developed Byne's Disease. Bruce Marshall tells me that the big wooden units
he uses at the Museum of New Zealand are all particleboard. These have been
sealed with polyurethane varnish and Bruce reports that there is no Byne's
at MONZ. I have sealed mine likewise and hope that will do the job.

Problem with these particle/chip boards is that formaldehyde is used in its
manufacture. Over time this releases formic acid, with obvious results.

I believe oak is another no-no for storage of shells, papers etc due to
acid emission.

Glass containers are another place where problems can occur. Over time some
glass tubes can chemically attack shells stored within. It depends of the
additives in the glass. I got 24 000 50x6mm testtubes at a technician's
sale. These are great for micros, except...after several years I have found
some specimens growing crystals. These are of two types; fine white hairs
which can completely hide the shell, and small white cubes. I don't know
what their compositions are or how to counter the problem, other than store
the specimens in absolutely dry conditions (absolutely impossible for me)
or replace the tubes with something else. Bruce Marshall says that
specimens over say 3mm won't be affected, while smaller ones will.
Apparently the expensive glasses are more likely to attack shells, whereas
plastic-stoppered cheap-glass containers may not.

Plastic tubes? These have poor optical qualities, tend to be bulky and
thick-walled and scratch very easily. And who knows, they may attack shells
too over time.

Andrew