I studded the outside walls in my attached house. Would I use duct tape to hold the insulation to the metal studs before rock?

You might try "unfaced" batts, they have no paper facing. They are cut just a little wider so they stick between the studs without falling out.

If you want or need a vapor barrier, after the insulation is in, you can apply plastic over the studs, held on with a thin bead on const adhesive, and a row of self tapping screws along the top, just hold it up.

Good luck

Roger

I have used 'Spray tack' adhesive to hold the insulation in place

Faced paper has the extra lip around the edges and by spraying the edges and the studs, giving them a few seconds to tack-dry, then applying them together has more than done the job.

Hope this helps,

KBC