Best way to prevent "racking" on a trailer IMO [of the boat- wearing a "cup" is best way for the sailor ;-) ]- support boat at inboard of front beams (this actually supports most of the weight of the boat) and middle of rear beam- I actually use an fixed inverted "L" angle on my rear mast stand and the rear beam is tied up to it (it's padded). I also have "U" sockets on the front beam supports so once boat is on front beam supports and rear mast stand is pinned in boat cannot "escape" from trailer except in cataclysmic accident (pun intended!).

Kirt