TonyG:
I have a metal box as you describe made by challanger which I think is a division of Delta but not sure on that. I actually use a 48" wide chest so that leaves space between the chest and the side walls of the bed and the wheelwells. I use that space to store things when traveling that I do not want sliding around in the bed. like chainsaw, fuel cans etc. Which leaves the box for tools, straps, parts whatever. Have it bolted through the bed floor with two lag bolts so that I can take it out of the bed in about 2 minutes by unscrewing the bolts when needed. It also allows me to put some 8 foot lengths of pipe, 2x4s whatever in the bed without taking the box out or resting them on the tailgate. This is the second vehicle this box has been in and still no leaks or dents after about 200,000 miles and 6 or 7 years.