I agree on the renting, since you won't be doing this often, and your car won't have the wear and tear.
If you want to go and not spend the extra money, take less. I did a month long cross country road trip with my husband and 3 year old son in our Subaru Outback, our bikes on the back and my son's bike trailer that took up half of the space in the back of the car. We even took all of our camping gear, which took up pretty much the other half, which we never even used. Didn't use the bike trailer either. So basically we wasted all of the space in the back and had our clothes and food in the back seat.