Grilled Chicken Breasts and holding

I am going to be grilling about 40 pounds of chicken breasts for a wedding reception. The breasts were marinated and frozen, now thawed. We are planning on holding them in electric roasters. What temp. should I grill them to, and how long can I hold them in the roasters without having jerky? It's probably half an hours drive to the reception. Any other tips would be appreciated.

Thanks in advance.