I'm with IAMICHABOD. My old girl gets about 7. Whatcha gonna do? I got the rig for $5800 and am into it less than $10k even after a boat load of work. I have exactly the floorplan I want, in exactly the size rig I want, I know the exact condition of the whole rig and I can take it to a shop without fear of getting gouged because I do know the condition. Best of all, it is completely paid off and I don't have to worry about compounding costs of purchase payment with whatever incidental maintenance or non-warranty repairs might be needed.
Only the most recent production models will give you "good" mileage, but the purchase price of a new unit in the size I want with the features I want, is a doggone fortune.
An RV is a luxury and you just have to understand that they are NOT going to get high mileage. I say, enjoy it for what it is and be happy.
Jose