Lift & secure the cargo floor w/the strap-hook made for it or remove the cargo floor altogether (hopefully you don't have the roll-out floor)...then remove the left piece that's below the cargo floor and next to the ULF (see #6 in diagram below). There should be a couple of nuts down in the wells that secures that rear left piece...this will give you access to the ULF. You can actually see the top left part of #6 in your pic.
Item #6 is secured by nuts (#4 in the diagram):
