The ornamental design for a storageunitassembly, as shown and described.
FIG. 1 is a perspective view from the top left of a storage unit assembly, comprising plural spaced-apart stacked tray modules, with the top handle extended;
FIG. 2 is a rear perspective view of the storage unit assembly of FIG. 1, with the top handle extended;
FIG. 3 is a side perspective view of the storage unit assembly of FIG. 1, with the right-side elevational view being a mirror image thereof; and,
FIG. 4 is a top plan view thereof.
The broken lines shown are for illustrative purposes only and form no part of the claimed design.