Obviously, you need to rent a hatchback, enough room to cook and sleep and carry the chicken for breakfast, the c is ok but the hatchback will do more...the yaris is a dead end...
Do they guarantee the car you want is available? Usually they only guarantee the class and size. As stated if you use your insurance you are out your deductible if accident occurs. I would rent the car. Let the rental company clean the bugs off.
FWIW, I recently had to make the same decision. We ended up renting a 2013 Altima. We averaged 38.1 MPG over 2,116 miles. It was an AWESOME road car - smooth, quiet, enjoyable... I'm obviously glad we went with it over the C.