It is commonly recommended to put water in your hulls to help hold it down in a hurricane, but this is with the boat on the ground, NOT on the trailer (unless you have full-length bunks for the hulls and can pad them nice and cushy). Normally, you want the boat on earth/grass, if possible, as opposed to asphalt/concrete. And, as brobru said, you probably should not fill it more than half full of water, because it is a lot of stress on the hulls.

If you don't have access to water to put in the hulls, I think it is a good idea to turn the boat upside down before anchoring it to the ground -- the wind cannot get as good a grip on it when it is upside down, and most boats are more stable upside down, less able to rock fore and aft and work free of their restraints.

If you are securing your boat on the trailer, it is also recommended to let some air out of your tires.