A method of fabricating panels includes providing an insert having an interior portion with a top portion and a positioning stop opposite the top portion, and an exterior portion including a fastener hem. Further, the method includes placing the insert in a mold such that only the fastener hem and the positioning stop contact the mold and centering the insert in the mold with the top portion and the positioning stop. The method also includes filling the mold with a casting material such that the interior portion is submerged in the casting material including the top portion, but some of the positioning stop is not submerged in the casting material, curing the casting material to form a panel on the insert, and removing the panel form the mold.