The only reason I put the sealer was to make sure no water came in and to make it look nice. And yeah I had some fires under there from the undercoating!
Not to sound like an ass but I weld in my driveway all the time without concern for others. There has only been one time someone has come up to me and it was a mother telling me to stop because her kids were staring. I then told her, this is private property, you don't let your kids stare into the sun do you? I may sound like an ass but I couldn't get anything done if I cared about the rest of the people around me. I would rather irritate some peoples eyes than have part of my truck come flying off the highway, killing me or someone else! Then again it is common sense to not stare at something like that.