Best way to raise, jack up, Sea Cracker?

[cdlong]

I want to start changing the rollers on my trailer. What is the best way to raise, jack up, the boat off the trailer? I don't have a spot were I can launch the boat and then replace the rollers. Due to finances, I have to replace them a few at a time.

[Bushwacker]

I've used a floor jack and a piece of 2 x 4 under the keel, or a bottle jack on outer frame and a 2 x 4 under chine to life one side at a time. The latter method will be a little more stable.