I repainted my trailer a couple of years ago. I was doing a fair amount of work on mine, so I needed to have the boat off the trailer for a couple of weeks. I supported the hull with a V-shaped block under the hull and stacks of wood blocking under the hull near the transom. Initially, I jacked up the boat using a couple of hydraulic bottle jacks (with short piece of 2x6 to spread the load) and then moved the trailer out from under the boat. I had to move the supports a couple of times as the trailer crossbars came close to the blocking, but it was really pretty easy. Then I left the boat where it was and took the trailer off to work on it.
I've heard of others pulling the boat off the trailer by strapping the transom to a tree, putting some old tires on the ground under the boat, and then pulling the trailer out from under the boat, but that made me a bit nervous. That, and I have a hard enough time winching my boat forward an inch or two on the trailer when the boat's loaded wrong. I couldn't imagine winching it all the way back on the trailer. I know others have done it that way, but I didn't want to try.
Good luck.
