Dont do that, I know a lot of the tray/res combos intend for you to place them on the res but they do make a stand for the tray or you can make one from 2x4's
I only say to do that because of the cost, down toward the end of flower when the plants are heavy + your medium and water *30-40 gallons* = disaster if the res buckles... your res is broken, your plants are hurt, at that point you need a solution asap. So instead of possibly going through that why not just make a $20 2x4 stand?
Im running ebb and flo now in a height restricted cab, it was tricky to figure out how i should run it but i eventually decided to run the res outside of the cab to give myself a few more inches of growth.