Almost all boat trailers are surge brakes.
UFP makes a good actuator that I believe most boat trailer manufacturers use.
Actuator. Brake assembly. You can find kits around and I'd have the tongue actuator welded on. Check your trailer to see if just inside the hubs you have square brackets on your axle. If not you will either have to take it and have the brackets welded on or buy a new axle with these brake mounting brackets.