Undercoating can weigh a bunch too. I've read where guys scraped off a whole car worth of the stuff and it weighed like 10 lbs, maybe more?

If a car is coated it covers a lot of area, not just the flat bottom but the wheel wells, inner fenders, nooks and crannies etc.

Not sure if that kind of savings is worth the hassle of removing it unless you are taking the unit body down to bare metal. Gotta sit there with a torch, putty knife and elbow grease for hours upon hours. Not sure if sandblasting takes off undercoating easily.

Same goes for seam sealer. My Duster has giant globs of it all over the car. It's a well-known fact that 'body in white' type factory racers had no seam sealer.