If your using your drybox as a passengers seat, then the foam deck is a must. No burnt butt cheeks here! Also, no spongey ethafoam that is uncomfortable, clammy, and ugly. With hig quality minicell foam, no negatives. The foam is installed when your drybox is made ensureing a perfect fit including beveled edges. The foam typically lasts as long as the drybox! No additional shipping when installed on the drybox.