Haven't used muck spreader of any type, we put poo in IBC tanks with top cut off, top up with water then take the liquid fert off at the tap, you could then just make up a small tank with holes in to put on the back of your trailer.
I have a set of the 10mm garden sprinklers set into a 1 metre straight length of water pipe, I pump the water/fert with a 12v diesel pump, all 15mm, I tow it with a westwood
Tip put a large ball of chicken wire on the inside of the tap to prevent blockages