i've seen the discussion thousands of times, the biggest thing you should remember, doors add a lot of rigidity to the truck, without doors, the frame and body will flex much more... so what i would do is make a half door, and fill in the bottom half with tubes... i made these pics a while ago...
start with a full door
remove the center of it, leaving the outer part intact, the part that's going to press up against the frame, and give some rigidity...
with all that gone, this door is going to be strong in some aspects, but still be rather flimsy... so i would add in some tubes in a manner like this... depending on how many tubes you put, you can use larger or smaller tubing...
http://i22.photobucket.com/albums/b339/g-
bus_rice/door2.jpg