Wow....lots of rookies on this subject. Many of the small trailers on the road have the self tapping screws insted of rivits. I have taken them out but when you tighten the screws back down, you run the risk if twisting the vinyl. If you try to heat the material down around the screws, you can only get it down so tight. Typically there is a slight bit of tenting around the screws. I prefer to not take the screws out because you are starting to affect the structural integrity of the trailer.
If you are working with rivits, there are several ways to work them. A rolle-pro is one way but it can be time consuming and frustraiting when you close off your air channels. I prefer using a 3M multipin punch tool (looks like a door knob w straight pins ..that give..along the bottom) a few taps over the rivit and then work it with a rivit brush. Then hit it with some heat and brush it again, this helps break the memory and keeps the material down.
The main thing is making sure that you are using the right material for the job.