The weight is about 60 pounds. I tried plastic boxes, but they cracked in the cold.
Underfloor storage is blocked. The drawers can be removed, but it is a PITA. In my case, it is not an issue as I have two batteries and the solenoid box for my rear winch under there, so the space is full.
The jack area is fully accessible, the drawers are set in due to the tailgates latch "bump" area, and that leaves the jack area in the clear. The right side houses a 120V inverter, 12v socket and rear winch connector. Left side has just enough space for a Sven saw and machete.
I did, at one pint, have the top hinged to lift up for easier access, but ended up screwing it down - once the welder and fridge are in there, there is no point.
I really like it - everything is stowed safely, but easy to get at, and I can fold down the rear seats and make a sleeping platform in a few seconds. (The Fridge, welder, etc are moved to a small trailer if I am sleeping in the Jeep so they are out of the way.)