heater box re-assembly

in the process of re-assembling the heater box. putting in a new core and evaporator. the styrofoam that sits underneath the evap is totaling destroyed. is it necessary, no i need it? what else would work? perhaps i could get it at the dealer, a week away and cost way too much.

thank you

Don't know its true purpose, Maybe insulation for the evap? or just to keep it from bouncing around int the box.... Maybe you could cut up one of those pool noodles to replace it?