I am also working on my 360 trying to take it out side for bigger walls. I have been following the progressions I used for my suicide roll and it's working great.
First, start on grass and lay a small backpack on the ground. Practice getting comfortable just doing the roll over the backpack.
Next, lay a leaf on the ground however far past the pack you want. Now throw it over the pack and past the leaf. (This way you are forcing yourself to throw it bigger just not super high.
Eventually, stack another pack on top of the first one and repeat. (This will gradually develop confidence doing the roll with higher and higher impact.)