Painting the bottom on trailer
I have done this a few times with my Cat 22. Several years ago I made adjustible supports out of 2 x 4's and 1/2" bolts to support the boat above the trailer (a Triad trailer). With the boat on the trailer, lift the stern using the trailer tongue jack (adjust the jack down and the stern comes up) and adjust and place the stern support as far under the stern as you can. Then, raise the tongue to lift the bow and adjust and place the bow support. Ease the jack down and the boat is now supported on the supports and should be a few inches above the trailer bunks. Remove the bunks and start prepping and painting. When done except for where the supports are, put the trailer bunks back and set the boat on the trailer again using the above process in reverse. Then finish the spots where the supports were. Also, with the boat suspended above the trailer, it's a good time to check the keel pin. Use a hydraulic car jack to lower and raise the keel. Due to the design of the keel, you can lower it until the pin is clear of the bottom and the keel will not fall out of the trunk. With the car jack pumped up, remove the 4 keel bolts. Ease the keel down until the pin clears the hull, remove the pin. I would suggest simply replacing the pin (1" silicon bronze) and keel bolts (stainless), rather than just inspecting. Keep the old ones for spares. As I said, I've done this a few times (and I need to do it again soon!) and it works.