Thanks for the info . I have started looking at the V8 . they have better towing and load capacity then the V6 . when I dig a little deeper it looks like the ecobust quickly loose there mileage advantage when under load or towing .Honestly I haven't weighed it yet but while jacking it up I could tell my jacks were struggling a little more. I still think I'm sub 2k but my F250 doesn't notice the extra weight much. I also didn't skimp out on materials. If you stick to 1/8" paneling and light material, you can keep the shelter light. If I were to do it again I would build the same layout, but with lighter materials. Once I get it weighed I will post my findings.
As for the fuel mileage you will suffer, but not as much as a full size truck camper. The profile of these are lower, the reason you don't have much headroom to start with, but I think overall its a better design to start with these shelters.