can you explain more about the pop rivet process?
Pop Rivets allow you to clamp 2 bits of metal together, even though you only have access to one side.
So all you have to do is drill the correct size hole through both bits of metal, put the rivet through, and then use the tool to pull the rivet up tight, which will clamp the two bits together. Once the parts are fully clamped, the rod through the rivet is designed to snap, meaning the majority of the rod ends up in the rivet tool, and just the ball at the end, which pulls up the inside of the rivet causing it to expand, stays in place... Sometimes this ball will drop back out, which is not a problem, as it has done it's job.
Basically you can use them where ever you want a semi permanent join between two plates, like you would a small nut and bolt, but could not get to the other side to hold a nut in place.
Downside is, normal pop rivets are not water proof, so you don't want to use them on the outside through to the inside, unless you put some extra work in and either seal them, or use blind rivets that have the end already sealed. Other thing is, they tend to be be best used where the two bits of metal are never meant to move in any direction, as they can work loose over time, if where they are mounted flexes, or twists.
Hope that helps.
The reason pop rivets are better for the rear door fix, over self tapping screws, as ideally with the screws, you should drill the hole right through, then open the hole on the head side, to a clearance, so the screws can then pull the back bit of metal up tight against the front bit. The problem here is, often when you try to do this, if you are not very careful, the drill goes right through, opening both holes up, plus the metal is not very thick, so not a lot for the screw to bite into to do it's job. Pop rivets go right through a clearance hole in both bits of metal, and effectively with the head on one side, and the expanding bit on the other side, pulls the two bits tight up against each other.