I've got a top tip for extra MPG when motorway driving- pick a HGV going somehwere 55mph+ (Eddies stobart trucks are best- limited to 56mph), then slipstream in behind them.
For added bonus, install a retractible harpoon on a wire rope mechanism in your bumper to fire onto the truck's rear to get a tow, then its infinite miles-per-gallon, retract when he goes off down the sliproad
