This request reminds me of "light, cheap, strong; pick two" I think the mileage thing is going to be your sacrifice if you want room for 4 bikes inside. Element, Ford Escape...will fill the bill but yes, mileage is going to be average.

If you are coming back to the states, can we still pick your brains about trips to Ambergris Caye? That's on the radar for our next dive trip.