The videos from Sailrite are good in telling how to deal with the high stress in the corners of Bermuda sails. However, the stress in the corners of a junk sail is just a fraction of that, so actually those videos shows how not to do it when making a junksail.

As long as the junksails are given a stout boltrope (rope or webbing), they seem to hold together well.

Cheers, Arne