Fenderwells, paint or undercoating

the body shop I'm taking the Dart to, mentioned blasting the undercoating out of the fenderwells and painting the fenderwells body color. Kind of on the fence on this, the undercoating is sold and seems to be holding. Just seems to me that paint would be more prone to chip in that area, leading to rust. Thoughts, opinions, which would be more original and how are yur fenderwells finished?
thanks
Aaron