Quite a long time ago there was a post where someone gave his tip on keeping the tie downs from getting loose. I've used it ever since and it's worked so far:
use a bungie to take the slack out of each tie down. After ratcheting down each tie down securely but not too much, loop a bungie around each tie down and to something else, even another tie down. this keeps the tie downs taught when hitting a big bump when the suspension can compress and the tie down hooks get loose from what they are anchored to. keeps all that from happening. Another important thing is to screw down two stacked 2x4s on each side of the front tire to keep it from kicking out.

past performance cannot predict future results. your results may vary.