Any progress? I have converted a Uhaul truck into a toy hauler as well! I sistered up two 2x4's and through bolted them through the truck box, ceiling to floor. They made a great mounting point for over head cabinets as well as added extra reinforcement for the sides. I wanted to reduce flex as much as possible so I did not have to worry about flexing of the windows or door we cut into the box:


View of the living area:




Toy hauler area:



One jeep iside, and one behind:




Also use to haul a Solo VEE


7.3 ltr diesel. Hot and cold water, full workshop etc.. A BLAST to build