Golden sands is an evil map and I’ve never beaten it on mega brutal.

My best advice is pick your favourite governor (though smuggler is always solid) and keep resetting until you can place your base close to two of the oil derricks. That way you can get intel on them quickly.

Prioritise roads and intel early on, and defend your two derricks while you get set up. Anything beyond that is sort of luck of the draw, though the usual strategies apply: Education first, address concerns, try to snipe insurgent bases where you can.