The biggest danger in boat/trailer tie downs is flutter and chafe. A fluttering strap will leave nasty marks on the boat. Same with a strap that rubs back and forth - it's just like sandpaper.
I put 20,000 miles a year on my boats/trailer and I make sure that
nothing is touching the hulls, other than the rubber trailer supports / cradles.
On each corner of the trampoline, I tie a loop of line around the sidebar. The "loop" is fed through the gap in the front trampoline down and toward the center of the boat and likewise at the rear of the boat. This gives me a place to hook in the "lever-over" type of straps that are permanently attached to the trailer frame. They look similar to this:
But they have a mounting plate on one end instead of a hook.
The result is a four-point tie down, nothing touches the hulls, and the boat rides rock-solid. Oh, yeah and it only takes about 5 minutes to attach the boat to the trailer for a 700 mile ride.
