underbody advice

I am in the same stage. Should I remove under coating or should I leave it. The guy doing the work to my car mentioned that if there are cracks in the undercoating then moisture could get in and rust the care from the inside out.

If you paint the undercoating will it seal the cracks? How well does paint stick to undercoating?

I am going to have the car media blasted. The body guy said I should do the underside done as well. Then we could just paint it black with Chassis Black.