It is a long reach to get to the center of your boxes through the side windows so it probably wouldn't be of much use anyway. For me it is enough of a reach to get in the side boxes from the windows.
Another question, which might be answered in your other pictures that I can't access from work, is how you secure the top access hatches? Seems like you would want something to keep those closed if something were to happen. Even a strap run across them might be enough it you have the tie downs for it and still easy to open.
yea I have long arms but not that long to get in there from the side windows.
as for latches for the top access, I have none right now. I have not looked to hard but I dont want anything that hangs down inside to catch on drawer stuff and i dont want anything on the top to snag my tool box and totes that i slide in and out. with the carpet on there it keeps them pretty tight for normal use. if I go do some serious off-roading I might just throw a strap across there.