Keep them in a cool dry place (but not bone dry). Heat and Ultraviolet light will drasticly accelerate the decompasition of plastics. They should be safe stored in plastic boxes or on acid free matboard. I have been looking for polyethalene foam "ethafoam" which is supposed to be archive safe. DO NOT store dice in polyurethane foam as the degradation byproducts of the foam will eat into the dice. A wooden display frame with a glass cover (preferably ultraviolet blocking would be a nice choice for a wall display. Polystyrene foam :styrafoam" is safe but tends to start crumbeling if you move the dice around. I have store dice in styrafoam for 10 years with no adverse afffect. Please note that any dice that are degrading will yellow the styrafoam as acid leaches out into the foam.

how about a scan of the dice?