We have had success with a soft aerodynamic cargo carrier that mounts behind a vehicle and virtually eliminates drag. When loaded with gear, it creates a shortened boat tail to improve rear air flow. On preliminary tests we have measured a small improvement in mileage. You can take that road trip, carry your gear and still have high gas mileage.
Aeropack is easy to load, mounts with out racks to hatchbacks and sedans.
Let us know if you are interested or would like to offer feedback.
Thanks,
Mike
AeroPACK Cargo Carriers