Thanks.
I'm trying to talk my dealership's service department into installing the sheet rubber I've purchased for this purpose. Maybe htis thread will hellp.
Up to you but I wouldn't glue anything to the plastics, it's not necessary. What I make covers as much as possible, doesn't interfere with anything for maintenance and is removable for cleaning or if you just want the heat in the winter. Don't know what rubber you're using either but this stuff's about as thick as you can go and remain pliable. It goes for $100 for a 10x10 piece online. For another $15....
If you insist on using what you have though, make sure to get enough for two. I've made a dozen patterns and the first one is going to suck no matter how good they are, it'll be close and usable but not perfect. Fine tune the fit with the second one and if it's cut right you won't need the glue.
As for how well it works, there's a couple out there installed and they say it helped with the heat and noise.