I actually did a rough calculation at one time of the weight addition from applying vinyl wrap to my Targa and it was only ~5 lbs. I removed the air conditioning, did a heater backdate, rear seat delete, and shaved the rear bumperetes to even that out...
The wrap on my rear bumper has held up very well without any visible heat effects. (This is on a '75 Targa with a 2.7.)