I let beast do the lightmap UVs, worked great, in fact better than custom UV2 since it wasn't always there. With beast it's just automatic, no worries. YMMV
just use beast the built in lightmapper of unity, with properly made lightmap UV sets, and a good lightmap red, it actually works really good. just make sure you got spilts and padding on your ligjtmap uvs anywhere where you don't want bleed.