So, there you go. Mileage will be similar in either a diesel pusher or truck/5th wheel combo. You'll need that secondary vehicle behind that diesel pusher to get around town. That's more insurance and maintenance cost, of course. A 35 foot fifth wheel will have the same space as a 40 foot diesel pusher. A truck and 5th wheel will cost less than that diesel pusher. You can drive the truck to work when you are not camping. You can drive that toad to work too. Maybe the car you already own is towable? Who knows?