I needed extra storage in the bed, besides the under compartment. So, I selected an add on case, which fits well, is relatively inexpensive, and mostly water tight (if in its normal position) looks like it belongs and doesn’t take much room (under the tonneau cover mechanism). It’s lightweight and won’t stand up to very heavy loads….but it meets my needs. It’s a Flambeau Linesman case, #7450AP. Being approx 43 inches at its top…its top lip just barely fits over the wheel wells, with the bed mat installed. I wanted the case to stay in place while driving, so I added a strip of 3/4” thick neoprene with adhesive on one side (to stick it to the bottom of the case). The neoprene also raises the case just enough for the top lip of the case to completely clear the wheel wells. The side of the case fits perfectly inside the wheel wells (its only the case top, that’s a bit snug). The case can easily be moved out from under the tonneau cover mechanism for access. By the way….Flambeau also makes other cases that may fit, but I chose this one to best suit my needs and be somewhat leakproof, from the occasional little bit of water that gets into the bed. See photos….case, case open, case bottom, case with added neoprene, case in the bed, and case open with contents.