[elhigh]

Going from the Ranger to the flatbed 250, you're giving up that convenient box into which you could pile your tools. You could consider some underbed toolboxes which would give you locking storage for your gear PLUS a handy anchor point for the many many acres of belly pan that truck would benefit from having.

How much of the flatbed's width do you need? Could you add locking toolboxes to the sides on the deck? You could create an ersatz pickup bed and still have 48+" between the boxes, and bring down a convertible fabric top to keep things smooth and aerodynamic when you don't need the extra headroom.

I'm actually sort of looking at this myself, my old truck's bed has seen better days. Going a route like this would retain the handy secure storage of a cap, if not all of the volume.

[edit]
Whoops, I see in your other post you've already addressed all this and more. Never mind me, carry on!