I would make a bolt on cover that seals the tank off from the interior for safety reasons. Adding an removable access panel for the pump/sender would also be a nice addition. The cover would allow you to use the back for storage because it will create a raised floor, right now I wouldn't want to put anything back there. It would add some structural value back to the body as would adding a nice HD skidplate. You could also incorporate some storage areas for spare axles, tools, a hi-lift jack/recovery equipment and other misc items around the tank cover. Two 5lb fire extingushers, one mounted in back and one up by the driver would also be a smart addition. The fuel filler area by the gas cap should be completely sealed off from the interior also.
I'm planning on doing this but with 1.5" lift shackles the springs sit 3" lower so the ground clearance gain is less then you have by the springs. I'm also mounting my rear shocks on my spring plates and going threw the floor with them and will be adding crossmembers for them which will kill my storage space anyways. The rollcage will also kill some storage area. Safety first.
A nice HD bumper would also increase the safety factor.
It's a nice modifcation, but needs to be completed for safety issues IMO...