Its pretty clear to me, by packing your own packages of oatmeal, bringing some bread, fruit and jam for breakfasts, and then making your own lunches, you'll each be able to save $18 per day, 3x18=$54, so about a days car rentals worth.
oh wait, you asked about the rack, sorry I got distracted by the last photo.....(I know, I know)
if the distances dont match up for the mounting points and you have to go the bracket route, I personally would put a solid bracket on the upper attachment point, so that where the weight will go the most (to the bottom mount) at least its well and truly supported there.