I use the ground screws but i also put my cat bows on my trailer and secure it to my trailer in 3 ways:
1. i use the winch and run it under the rear trailer beam (where the tag is) and up to my dolphin striker
2. i use a tie down line that is on my trailer and attach it to my port stay and do the same on starboard
3. i use a tree auger (screw) behind the rear beam and tie the cat port/startboard beam area to the auger.
so my boat is secured very well on all 4 sides.
Of course if the cat next to you doesn't tie down,... it can fall on you...
about the trailer blowing away.. my steel trailer weighs 3 or 400 lbs.. i lower the 5th wheels and it would take a tidal wave to move it..
That being said we recently had a guy leave his h16 on the trailer... and it was pushed in the gulf overnight... not by wind or water.... I had recently asked him to use a ground screw at the least... which he balked at.... (thats his trailer mast cradle sticking up by the starboard bow)