I am going to install a Harken 241 swiveling cam cleat base and will need a backing plate on the inside which is not supplied or hinted at by Harken. What has worked for those of you who have installed one? I plan to install a cockpit 5" access port on the left side to assist in the installation on a pristine 1970 boat. Also installing a hiking strap which will also need a backing plate I bet.