Do you need to isolate an aluminum radiator?

A coworker (who is a hot rodder and has built many cool rides and I trust his info) told me that he has cracked tanks on aluminum radiators by bolting them solid to the core support. He suggested using rubber isolators. I'm not opposed to this, as it does eliminate stray current which can corrode aluminum. My main concern is has anyone else ever experienced a cracked tank from not being isolated?