Agree with the use of the boat stands. When we were borrowing a trailer to haul the boat every year, we would jack the back of the boat up with a floor jack, and build cinderblock towers topped with wood 6x6s to support the transom corners. Lower the boat onto the towers, and jack the bow up forward until the trailer cleared. Then, slowly creep the trailer forward until the axles were near the jack; support the bow with jackstands and move the jack aft of the rear crossmember. Trailer pulls away, lower the bow onto another set of keel blocks forward with the jackstands continuing to support the bow.
Now that we store the boat on a trailer, the jackstands still come in handy to take some of the load off the trailer as it sits for the whole winter season. Also, they stabilize the boat a bit if you're climbing on and off to get off-season projects done.