I hate to say it, but the cauliflower roots are more than likely too deep rooting for a combined nutrient tank and reservoir system. Spinach is pretty ideal along with other leafy greens and... strawberries! Mmmm... Anyways, these systems are designed more for shallow rooting plants. Otherwise, you could maybe try the fiber mats they use for the NFT systems. You could try just laying it on your mesh net. Good luck.

I have aero systems that are 16ft long x 2ft wide and deep, they`re not restricted to shallow rooting plants. The main issue with cauliflower is the above ground space, they need a good 30" x 30" plant spacing.
If you`re dead set on "trying" to confine the roots, use a frame coveed with a fine silkscreen printing fabric. Be aware that the roots will find the smallest gap around the sides so the frame will have to be a very good tight fit.