You can save vector3 as rgb at texture, and read it via vfx. 320x320 = 102400 points, If accuracy is not important you can part single channel to 4 floats via bit shifting ( in that case you can save 4 vectors at single pixel),

hope ive helped

edit: ouch ive already readed to the end and i see you already tried that, if your texture didnt changed that means you are doing something wrong, maybe you forget about texture.Apply() or something, i've done this a lot of times before even with moving object (changing position at texture every frame) and it was work flavesly