If you’re hiring a car for a group of climbers, but it’s too small to hold all the luggage, i.e. you paid for the cheapest car you could find, then take along a soft rack. If you turn up with four people and a ton of crap, they might refuse to rent you the car, in order to force you to upgrade; so have one person get the hire car, leaving everyone with the luggage at the pickup point, then drive back and load up. Strapping on two big duffel bags works best, but use your foam mats in-between the bags and the roof, so as to avoid scratches (lift the bags on and off, don’t pull them). Don’t crank down the bags down so hard you damage the roof and put all the heavy stuff in the boot or footwells. If you do create a depression or dint in the roof, then pouring on boiling water, or leaving it in the hot sun, should pop it out. Don’t leave the bags on the roof when the car is left alone, and write your name and contact details on the bag, in case you lose one on the freeway!