Does overkill need to be glued down to the car floor, or can you just lay the normal carpets over the top to keep it in place and a bit of tape?
Or does it need to be held to the body of the car evenly to work well?
I assume as it is just foam then loose is ok?

Not sure but i would stick it down just to make sure, i didn't use the SS spray glue, i just bought some cheap stuff from my local DIY shop