For long-term storage I would avoid esterfoam in favor of lining the crate with 2" extruded EPS thermal insulation and cushioning the artworks with 2" ethafoam bumpers inside the EPS. Trays, dividers or portfolios for the prints should be made with archival materials. Other precautions can be taken from there, such as lining the EPS with Marvelseal before installing the ethafoam bumpers.