[Chimera-users] saving 2 maps for difference

I have 2 density maps, and use the "fit in map" function to best align the 2 of them. I'd like to use this fitting to create a difference map, but the original maps are not the same size. Does anyone know how to save both maps to the same grid in Chimera? For now I've been using the "subregion selection" tool in combination with "resampling voxel size", but if someone has a more direct method it'd be much appreciated. Thanks, -gabe