Mark;
As a former but retired sailboat dealer who has positioned boats onto trailers, I will speak from experience and knowledge.
first, I am not sure if your boat is a keel or swing keel. Brain S. hit on some main points. If this is a keel boat, the weight of the boat will be supported by the keel sitting on a keel tray. If that is the case, make sure the keel tray is fine but if not, then replace those boards. If it is a metal keel tray, make sure you add carpet so the boat will not slide as it will with a keel sitting on metal in transit is not secured correctly.,
If it is a swing keel, the weight of the swing keel will rest on the keel tray while the rest of the boat is supported by the bunk boards. Again make sure the bunk boards are not rotten and replace accordingly and apply new carpet (outdoor carpet of course) and make darn sure that the bunk boards are aligned with the curvature of the hull.
With all boats, you want for safety appx. 10% of the total weight of the boat and trailer on the tongue on the tow vehicle. If not, you will experience swaying more so on a single axle vs. a dual axle. So make sure the boat is positioned on the trailer but at the same time look at the tires(make sure they are inflated to specs) that the tires are not dry rotted or damaged.
Replace the winch strap if rotten or if it is line, that too if rotten. Make sure you have a safety chain for the bow eye as a back up but if not, use a heavy duty line. If chain is too long, you can always twist it to shorten it up. Make sure lights are working.
Most dual axle trailers will have brakes and if so insure they are working. Some states require inspection so check on what the requriements for titling and registration as well as inspection.
Always use a tie down across the cockpit only and twist the line a couple of times coming over the cockpit combing down the side to keep the strap from flapping in the wind. Go about 10- 20 miles stopping to inspect make sure all it tight and not loose.
Once you take ownership of the boat, liability will rest with you. Hope this helps and if you have any further questions, feel free to contact me via this forum's email.
crazy dave condon