For sound and heat resistance there is a padding out there that you install between the floor and the carpeting that is a foil backed insulation. Check with your local auto parts store.
Short answer, NO you do not NEED undercoating.
It will depend on how much undercoating you are wanting to rubberize.
No.
starting at $150
according to the info i read on the back of my can of undercoating, it only takes 10 minutes. I'd give it a 1/2 hr myself.
For Sound, lead or massive concrete; for Heat, fibrous non-conducting materials such as fibreglass and asbestos; for Electricity, ceramics, glass, and plastics.Note, a vacuum is an almost trivial answer for both heat and sound.
No, undercoating should last for years.
Light,heat and sound are all energy.
Maybe so you can see where you need to patch it up... maybe...
heat energy + sound energy
Sound doesn't travel in heat. It travels in a physical medium.
heat, sound, and light