Agreed. I found the drawer video posted above early on, its definitely an ideal solution. You might be able to run three if the middle one was run in-line with the center console/loss of foot area for middle passenger.
These cases do have a rubber gasket and advertise it to "prevent against water and dust damage". I'd gladly throw them in the bed / exposed to elements but probably wouldn't be putting anything inside them I wouldn't be ok with getting water/dust damage in the even the seal(s?) fail.
Good points. Just went out and measured... 6.5" clearance at the back of the seat before the storage bin...almost exactly. Right around 60" width to work with horizontally... time to get creative. lol. I really wanted to invest in the Milwaulkee Packout system instead, but I think it will stick out a little too far (2.3" additional)... What I'm thinking about is getting the complete system that has the rollers and larger box and setting it up so I can put the large bench seat down and the little bench seat up with the large roller perpendicular to the underseat cases. Could still haul 2 people that way and have a ton of modular/mobile storage.
So glad I came across this post - it's exactly what I needed instead of a drawer!