Always ways to support....
...the keel if there is none. One boat hauler taught me a great way that I still use till this day. Get a HEAVY DUTY ratchet stap, hook to both sides of trailer with stap under keel, then tighten as much as you can. If there is a cross support of the trailer under the keel, you can also build support with adding wood between keep and cross member. These are things that will work just fine for a one time trip, but would do a "real" support if you are keeping the boat on the trailer for any length of time.