I have had the same problems with chrome over thin metal like the intake pipe, valve covers and a bike fender. I have seen it with both super chrome and xtreme chrome. On thinner substrates I have started putting on two coats of chrome and have had no more problems. I put the second coat on right after the full cure of the first coat. Just be careful and dont lay the second coat on too thick.
Jason
www.autocyclepc.com