Dimension needed

[dcobbett]

My roller trailer for my 1976 20SF is in the driveway and I'm in the process of making some repairs and changes to the arms, etc. Boat is on the mooring and I need to know how wide the second bottom panel is. I know it starts at the inside face of the tank coffin, but I can't remember the distance (out) to the next step. Thanks in advance.