I don't think it weighs but only around 350 lbs for 1 cu yd.
This is how I came up with that.
13 - 2cu ft bags equals 1 cu yd.
I would GUESS that 1 bag weighs about 25 lbs. 25 x 13 = 325.
Then add a little for wetter mulch. Total = 350 lbs
It depends on how high the sides are on your trailer. If it is 5 x 10' as your tag says and the sides are 2' high that would be 100 cubic feet or 3.7 cubic yards. Unless the mulch is sopping wet it would be within the weight capacity of the trailer. If you don't have trailer brakes and you're not pulling it with a heavy duty truck you might have problems stopping.