Man -that thing is a monster slide on. I'm going the other way. Just sold my 6 1/2 foot slide IN pop up camper from my short bed F150. Plan to build a camper conversion in a 136" PM high roof diesel. It should have about 1 and a half times as much room as my pop up and I expect it to get over twice as good fuel mileage.(12 mpg gas to 26? mpg diesel?) The bonus for me is I can walk back to the bed, no pop up to raise, no high bed to climb up to, etc. You will gain the ability to park anywhere and move nimbly, but it may feel small.
Yeah, I would like to see a little better fuel economy too. I usually get 12 mpg in the Fuso weighing about 12,000# although I took a 3000 mile trip towing 8 scooters and still did about 11 mpg while weighing in at almost 19,000#.