I'm looking at trying to create a tie-down lashing for a liferaft container out of 2" seatbelt webbing. It would be attached to a frame with shackles, basically, and kept under tension to hold the container in place. 2 questions:

1) How would one go about modelling the webbing under tension? There are several different containers I'll need to make webbing for, so being able to do it using configurations would be nice. The webbing is under tension, so it will conform to the top of the container but not to the sides, as it splays out to the attachment points.

2) What's the best way to mate two shackles together? The mating surfaces would be the loop ends of the shackles, not the pins. I've tried using tangent mates but it creates some very odd behaviour.

Thanks for any help!