We are going to get an insert and have one question (did a search and did not find anything), we have a pre fab fireplace by the way. My question is when measuring for the minimum clearances I am good everywhere but the depth. Are you supposed to measure the inside of the box with the firebrick panels in or out? It looks like I am going to be 5/8" short on the depth with the panel in but if I could remove the back panel that would give me an extra inch. We are looking at the PE Pacific insert. Any suggestions would be greatly appreciated.