I used the TSC box too and used
@TerryH 's most excellent video. He used back packing type straps and buckles originally (don't know their real name) and has switched to cam lock type straps with better luck (I've had no trouble with the originals). You could also use turnbuckles if you put the D-rings high enough in the TSC sides like Terry's.
Best photo I have but it doesn't show the tie down method.
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