Whichever way you go, you will still be climbing in and out to get something. Nothing you want will be within reaching distance of the door, guaranteed. Put in plenty of shelves as the floor will fill up and be cluttered and be a pain to climb over. Put the bigger stuff and stuff you use all the time like power tools close to a door. jb is right about some type of headache rack for the front seats. There will always be some boards or pipe aimed and poised to impale somebody in the back. Put some racks on the inside for carrying boards to keep out of the rain. If it is big enough to slide in drywall or plywood, then have some type of latch at the top to hang over and or a rack to hold it up. Bumper brackets and a bracket on the passenger for long pipe and boards may be easier than trying to lay them on top when you only have a few.