to feed 100 people.

I've done 3 sheet cakes before (I normally get tiered cake orders so I don't do many sheet cakes).

1 cake I did last week was a 1/2 sheet cake and the darn thing almost split down the middle (I blame myself-didn't have a sturdy enough board under)

For a cake this big (18X24) do they make thick cake boards for this size or am I better off using a piece of wood?

Triple up the cardboards and it should work.