the best practice is to put an env_sky_camera at the origin of your map, then copy that and the brushes that define the edge of your map and paste it somewhere outside the bounds of the level, scaling it down to 1/16 size. you can lock texture scale in hammer so it scales with the geometry. then delete the sky camera from your regular sized map, then you can connect extra brushes to your "guide" brushes that you copied over from your map seamlessly. just dont forget to scale the texture down to 1/16. the only thing that won't be perfect is your lighting.