I know 20 MPG would be dreaming, but I'm thinking somthing like 16-18 unloaded would be ok.. even 14 wouldn't be that bad, don't have very far to go.. dual tanks on an F-150.. I could go for a while in between fillup's but they'd be what $100 fillups?
I remember when my dad had his '97 F-150, with the big 30 gallon tank.. always complained about the $50 fillups.. but it was around that time my parents were complaining about $1.50 gas