There is a certain freedom and responsibility involved when working on a museum piece.The freedom comes in knowing that once it is in the case it will be subject to the best conditions possible and also will be maintained in the future. Therefore the use of some materials such as pastels is a realistic consideration,
knowing they won't be handled a lot in that setting.
Also painting figures is a lot easier when scale distance,lighting and angle of view can be established ,especially in shadowbox work.
The responsibility lies in making sure that only the finest materials are used and that they will stand up to what can be the very polluted atmosphere of an enclosed case.To be on the safe side I have recommended that they allow for some air exchange.
Metal is especially subject to corrosion so I seal it well and try not to use incompatible materials together.
I have had a mixed media HMS Victory in a ventilated case for almost fifteen years now without any problems with corrosion or dust.Also the only material I used that doesn't have long standing durability record is a little super glue on the rigging.(I have since developed an allergy to it so that hasn't been a consideration for awhile now.)