I never user straps. I don't like them. We use rope and a trucker's knot. These will only come undone when you untie them or the rope breaks. As you pull tension on the rope, the knots get tighter. I also use the suspension as a point for constant tension.
I've had machines rock back and forth and the rope loose tension, but never come off the machine.
This picture is almost identical to the knot. Step 3 is modified for easy removal. Instead of having the last bit of rope pulled through, i double it back and pull a loop through. This serves for easy removing of the knot. A quick snap of the rope will undo the entire knot.
http://www.paddling.net/sameboat/Images/knottruck.gif
I just wanna go fast. If your not first, your last!!
Reproducing the Tecate CDI. Contact me if you need one. I'm most accessible on FaceBook. You can find me on the 1984-1987 Kawasaki Tecate KXT250 Group.