As others have said, no one knows for sure how the mail chausses were attached, but the likelihood is that they were simply attached to a belt of some kind, similar to how the fabric clothing chausses were pointed to the braies.
I use a belt for mine, and I can share my my experiences with this. I've found that it works best to attach at the sides, like fabric chausses, rather than the front.
Also, the belt needs to be beyond tight. Not just "wow, kinda tight"... but all the way into "OMGWTF TIGHT!" territory.
As in, however tight I would make it for pants, I need to tighten it about 6" beyond that, minimum. This is quite uncomfortable at first, but after a while you get used to it, but it will ache after a few hours.
If not tightened enough, they'll seem comfortable at first, but after maybe an hour they will become extremely painful, because the belt can work itself down over the corners of the hips.
Part of the problem with mail chausses is that they have decent amount of weight, and there is no natural structure to your body that holds the weight, since they taper downward. With every step, they want to work their way off your legs. You can mitigate some of this by lacing it in a variety of places, particularly right below the knee (top of the calf muscle). A tight lace here will help keep it from riding down too much.