@jjvw - this box I have is perfect (it's only 32" wide). I got the b idea from
@MountaineerTom. See my thread in the Gear area, I linked his photos there. It holds quite a bit! The only thing I did not like about it was the cost but I had some prime rewards points so I did not mind. It's all Aluminium and only 17lb and after I saw it in person I was happy that I bought it.
UWS EC20012 32-Inch Gloss Black Heavy-Wall Aluminum ATV Storage Box, RigidCore Lid
https://www.amazon.com/dp/B077BXS2JS/?tag=wranglerorg-20
The box is sitting on 4 hockey pucks and just barely clears the seat rails. I have it bolted down to the seat rails, see photo below.
I removed the latch/lock that came with it and installed a Bolt one (link below). The bolt latch "learns" your Jeep key. This way you don't have to carry an extra key.
Also, as a bonus for me, the recovery boards I bought a while ago for behind it just about perfect with a bungee cords around the handles. I'm really happy with this box.
Bolt 7022699 Toolbox Latch...
https://www.amazon.com/dp/B007VA6PPG/?tag=wranglerorg-20
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