I believe you should Hysol the stringer to the backside of the door frame. It will stay in position by itself due to the tension.

The door latch strike plate is not in the kit and you are on your own. I did mine like the factory SLSA- After you have covered and painted the fabric that wraps over the bottom door frame, make a thin aluminum channel that snugly fits over the bottom door frame and clamp and Hysol it on. Make it the full length of the bottom frame and leave it unpainted. It acts as a scuff plate for getting in & out of the cabin and also serves as a strike plate for the door latch. The factory also puts a similar piece of channel over door frame that angles up from the bottom alongside the seat for extra scuff protection. It looks good done this way.

Jim