You would likely be best served making a cover out of 1" netting, attaching some synthetic jute, and then natural veg. That will be the lightest ghillie for grassland. Perhps just building a viper hood would be the best option for maneuverability. Most premade suits are a fine mesh, which will trap a layer of air underneath and can be uncomfortable in high humidity. Paired with a decent coloured long sleeved wicking layer, it should blend in well enough.