I purchased a double decker built in oven from Goodwill and separated the two ovens. One of the Valley Metal club members purchased the bottom half. The bottom had manual controls and the top had digital. Guess how long the digital stuff worked ? I retrofitted with a process controller and a couple of SDR's. The initial installation had the SSR's inside the face of the oven at the location that they are now mounted on the outside. The face was not enough metal to heat sink the SSR's and adding a muffin fan did not help. The cooling problem I was actually chasing were defectively designed SSR's from china. (I don't have anywhere enough respect to capitalize the name of the country, just sayin')