What kind of dock are you talking about? How athletic are you and how tall?
I single hand a C&C 35-1 on and off a floating dock and other docks in good conditions. My boat has midship gates and I run 35'' lines from the bow and stern to the gate. The extra line from each is piled in the gate opening on the deck and the bitter end of each line is layed over the lifelines on each side of the gate.
When the boat is close enough to the dock I step off dragging the two lines far onto the dock. Then I turn and secure the one that needs it the most. While a midship line would work the boats bow might blow off in certain conditions and require a bow and or stern line anyway.
I am quite old and lame but I can still do this because I think I can.
I do it 90% the time alone too. I applaude you for doing it even when you feel old and lame. I am 52, I plan on doing this as long as I am left on the earth. The midship lines are a lifesaver. I havn''t had a problem since I started tieing that way when I come into my slip. And it''s 90% of what I have read here that started me doing it that way. BTH sailing yesterday was a JOY. 15-20 knots of wind 5-6 feet off the water the surface was like glass but the sailing... WOW.
My boat has an aluminum extrusion toe rail. Not sure if they are on Catalinas but I think so. Anyway a previous owner had added midship cleats to the toe rail using a regular cleat anb and right angle of aluminum or steel. Bolt the right angle to the toe rail and to the cleat.
You can find purpose made cleats that attach to toe rails on the net, I haven''t searched here, but they should have them - or be able to order them.
You want a good midship cleat for spring lines, guest lines, etc.
One other option... if you only need this cleat for docking... I bought a set of cleat that fit onto the track that runs fore and aft for the jib sheet blocks... it lets me position the cleat anywhere I want along the side of the boat.
Wouldn''t be good for a permenant dock line, as the chaffe over the toe rail would be too great, but, it would work for getting on the dock.