You can attach the panels in a number of ways.
We have customers who have had great success with a double sided upholstery/trim style tape (foam type) - very sticky!
Many have used a hidden, or 'blind' fastener (I have heard them called 'Christmas tree clips' before) on the backside of the panel, located into a requisite hole on the door shell.
Others have used an oem approach, with a visible screw and washer like a factory setup.
Here is some at speed At a Cobra Mustang event at the best track I have ever been to VIR. I had to tape up the turn signals so I would not break the glass