Making Light Maps in Blender

Hi, I've working on a map of Helm's Deep in UDK. I'm almost done with the models for exteriors. But I've been having problems with light map bleeding/seams. Does anyone know of any good tutorial for making light maps in UDK? I hear that we need to use grid snapping to avoid the seams. But all I can find in Blender is pixel snap. I'm not quite sure if that helps. So if anyone knows a proper way to make lightmaps for UDK in Blender, please do let me know. Thanks.