I RTV attached my 18" f/4 to an 18 point cell with no observable problems. I did however minimize the cantilever from the cell triangles to the mirror rather than using weldnuts. I'm in the process of removing the RTV and replacing it with Dow832 after it detached in a cross country trip...likely upside down the whole way. movers... jtm (www.jtmiller.com)