are fairly wide as can be seen and are arranged in a desired orientation so that they will receive the vertically oriented burn in boards a pair of silicone rubber seal sheets indicated at 56 and 57 are then put into a laminated or sandwich construction each of the sheets 56 and 57 has a plurality of slits as indicated at 56a on sheet 56 and at 57a on sheet 57 that are in alignment with the slots 55 in the backing sheets 53 and 54 the slits are merely slits in the material and when they are aligned with the slots 55 which are wider than the slits and the unit is made into a laminated or layered structure the edges of the slits will have to yield out of the way when the burn in boards are passed through the slots 55 of the wall module 13 the sandwich construction is made by placing the sheet 56 up against the edges of the support bars 45 and then clamping the sheet 56 by in turn clamping a backing sheet 53 resilient or elastomeric seal sheet 57 and the sheet 54 together and holding them in position clamped together with suitable screws or fasteners that pass through these sheets and engaged the seal support bars additionally the support sheets can be supported by using suitable brackets 60 and 61 as shown in fig1 to tend to clamp the edges similar brackets can be used along the top and the bottom where they will clear the burn in boards 35 the sheets 53 and 54 can be stainless steel fiberglass a polyimide or other rigid high temperature tolerant material as shown in fig2 two.