Use the plastic outer pieces w/ attached flexible gasket material cut to length, comes in white or dark brown.
Sometimes you will want to build up the door outer frame w/ 1x so that there is more overlap, you want ~1" of overlap at top and sides.
On my unheated garages I use a single piece at the top and sides, on the heated garage w/ a 3" insulated door I doubled the gasket at the top and sides w/ ~1.5" overlap and used a third gasketed piece on the inner sides. It's toasty in there all winter.
