I just finished this insert for the shower in our new 16XRB.
Sterilite Wide 3-Drawer Cart, some MDF, 2 plastic socket flanges, pipe clamps and PVC pipe. Bottom drawer left out and the space will be used for shoe storage.
Shirts on the bar, shorts or pants on the top, my socks and stuff in the top drawer, wife's socks in the second drawer and shoes and flip-flops on the bottom. The MDF is the decking which fits inside the rim of the shower pan.